Power supply system, transportation apparatus, and method for controlling power supply system

ABSTRACT

A power supply system includes a power transmission electric circuit via which an electrical load is connected to a first energy storage and to a second energy storage. A first charge rate indicates a charge rate of the first energy storage. A second charge rate indicates a charge rate of the second energy storage. A ratio of a first electric power amount of an electric power to be supplied from the first energy storage to the electrical load and a second electric power amount of an electric power to be supplied from the second energy storage to the electrical load is changed in accordance with the first charge rate at least in a first mode among the first mode and a second mode. The second electric power amount in the second mode is smaller than the second electric power amount in the first mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2016-066922, filed Mar. 29, 2016,entitled “Power Supply System, Transportation Apparatus, and Method forControlling Power Supply System.” The contents of this application areincorporated herein by reference in their entirety.

BACKGROUND 1. Field

The present disclosure relates to a power supply system, atransportation apparatus, and method for controlling power supplysystem.

2. Description of the Related Art

Power supply systems of this type, as disclosed in Japanese UnexaminedPatent Application Publication Nos. 2014-187757 and 2015-70726, forexample, are known in the related art.

Japanese Unexamined Patent Application Publication No. 2014-187757proposes a system which is capable of supplying power to an electricmotor for a vehicle by using two energy storage devices, namely, ahigh-capacity energy storage device (a battery) having a relatively highcapacity and a high-power energy storage device (a capacitor) having arelatively high upper limit on power that can be output. In this system,power is exchanged, as appropriate, between the two energy storagedevices so as to set the state of charge (SOC) of each energy storagedevice to be close to an SOC center that is set in accordance with thevehicle speed.

Japanese Unexamined Patent Application Publication No. 2015-70726discloses a technique for a hybrid vehicle including two, high-capacityand high-power energy storage devices, for supplying power from only thehigh-capacity energy storage device when the required output for poweris less than a threshold and supplying power from both energy storagedevices when the required output for power is greater than thethreshold.

SUMMARY

According to one aspect of the present invention, a power supply systemincludes a first energy storage, a second energy storage, a powertransmission electric circuit, and circuitry. The first energy storagehas a first power density and a first energy density. A first chargerate indicates a charge rate of the first energy storage. The secondenergy storage has a second power density higher than the first powerdensity and a second energy density lower than the first energy density.A second charge rate indicates a charge rate of the second energystorage. An electrical load is connected to the first energy storage andto the second energy storage via the power transmission electriccircuit. The circuitry is configured to control the power transmissionelectric circuit in a first mode when the second charge rate is higherthan a second switching threshold while controlling the powertransmission electric circuit in a second mode. A ratio of a firstelectric power amount of an electric power to be supplied from the firstenergy storage to the electrical load and a second electric power amountof an electric power to be supplied from the second energy storage tothe electrical load is changed in accordance with the first charge rateat least in the first mode among the first mode and the second mode. Thecircuitry is configured to control the power transmission electriccircuit in the second mode when the second charge rate is lower than afirst switching threshold lower than the second switching thresholdwhile controlling the power transmission electric circuit in the firstmode. The second electric power amount in the second mode is smallerthan the second electric power amount in the first mode.

According to another aspect of the present invention, a method forcontrolling a power supply system includes detecting a first charge rateof a first energy storage having a first power density and a firstenergy density. A second charge rate of a second energy storage isdetected. The second energy storage has a second power density higherthan the first power density and a second energy density lower than thefirst energy density. An power transmission electric circuit iscontrolled in a first mode when the second charge rate is higher than asecond switching threshold while the power transmission electric circuitis controlled in a second mode. A ratio of a first electric power amountof an electric power to be supplied from the first energy storage to anelectrical load and a second electric power amount of an electric powerto be supplied from the second energy storage to the electrical load ischanged in accordance with the first charge rate at least in the firstmode among the first mode and the second mode. The electrical load isconnected to the first energy storage and the second energy storage viathe power transmission electric circuit. The power transmission electriccircuit is controlled in the second mode when the second charge rate islower than a first switching threshold lower than the second switchingthreshold while the power transmission electric circuit is controlled inthe first mode. The second electric power amount in the second mode issmaller than the second electric power amount in the first mode.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 illustrates an overall configuration of a motive power systemaccording to an embodiment disclosed herein.

FIG. 2 conceptually illustrates how the respective capacities of a firstenergy storage device and a second energy storage device are allocatedfor use.

FIG. 3 is a flowchart illustrating a main routine process executed by acontrol device.

FIG. 4 illustrates a map used in a control process when power issupplied to an electric motor in a charge-depleting (CD) mode.

FIG. 5 is a flowchart illustrating the control process when power issupplied to the electric motor in the CD mode.

FIG. 6 is a flowchart illustrating the control process when power issupplied to the electric motor in the CD mode.

FIG. 7 is a flowchart illustrating the control process when power issupplied to the electric motor in the CD mode.

FIG. 8 is a graph exemplifying the relationship between respectivepercentage shares for the first energy storage device and the secondenergy storage device and amounts of heat generation.

FIG. 9 illustrates a map used in a control process during regenerativeoperation of the electric motor in the CD mode.

FIG. 10 is a flowchart illustrating a control process duringregenerative operation of the electric motor in the CD mode.

FIG. 11 illustrates a map used in a control process when power issupplied to the electric motor in a first charge-sustaining (CS) mode.

FIG. 12 is a flowchart illustrating a control process when power issupplied to the electric motor in the first CS mode.

FIG. 13 is a flowchart illustrating a control process when power issupplied to the electric motor in the first CS mode.

FIG. 14 illustrates a map used in a control process during regenerativeoperation of the electric motor in the first CS mode.

FIG. 15 is a flowchart illustrating a control process duringregenerative operation of the electric motor in the first CS mode.

FIG. 16 illustrates a map used in a control process when power issupplied to the electric motor in a second CS mode.

FIG. 17 is a flowchart illustrating a control process when power issupplied to the electric motor in the second CS mode.

FIG. 18 illustrates a map used in a control process during regenerativeoperation of the electric motor in the second CS mode.

FIG. 19 is a flowchart illustrating a control process duringregenerative operation of the electric motor in the second CS mode.

FIG. 20 is a graph exemplifying patterns in which the respective SOCs ofthe first energy storage device and the second energy storage devicechange over time.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

An embodiment of the present disclosure will be described hereinafterwith reference to FIGS. 1 to 20. Referring to FIG. 1, a motive powersystem 1 according to this embodiment is a system mounted in a vehicle(more specifically, a hybrid vehicle) that is an example of atransportation apparatus. The motive power system 1 is an example of apower supply system according to the embodiments disclosed herein.

The motive power system 1 includes an internal combustion engine 2, anelectric motor 3, an electric generator 4, a first energy storage device5 (a first energy storage 5), a second energy storage device 6 (a secondenergy storage 6), a power transmission circuit unit 7 (a powertransmission electric circuit 7), and a control device 8 (circuitry 8).The internal combustion engine 2 and the electric motor 3 are capable ofgenerating motive power for driving a drive wheel DW, which serves as adriven load, to rotate. The first energy storage device 5 and the secondenergy storage device 6 serve as power supplies for the electric motor3. The power transmission circuit unit 7 performs power transmissionamong the electric motor 3, the electric generator 4, the first energystorage device 5, and the second energy storage device 6. The controldevice 8 has a function of controlling the operation of the motive powersystem 1.

The internal combustion engine 2 transmits motive power generated byfuel combustion to the drive wheel DW via an appropriate powertrain todrive the drive wheel DW to rotate. The powertrain in the motive powersystem 1 in the illustrated example is configured to transmit motivepower generated by the internal combustion engine 2 from an output shaft2 a of the internal combustion engine 2 to the drive wheel DW via aclutch 11 and a plurality of gears 12, 13, 14, and 15 in sequence. Theclutch 11 is selectively operable between a connected state for makingtransmission of motive power feasible and a disconnected state fordisconnecting transmission of motive power.

The electric motor 3 corresponds to an actuator according to theembodiments disclosed herein. The electric motor 3 transmits motivepower generated through the power-running operation when supplied withpower to the drive wheel DW via an appropriate powertrain to drive thedrive wheel DW to rotate. The powertrain in the motive power system 1 inthe illustrated example is configured to transmit motive power generatedby the electric motor 3 from an output shaft 3 a of the electric motor 3to the drive wheel DW via the plurality of gears 16, 13, 14, and 15 insequence.

The electric motor 3 is also capable of performing, in addition to thepower-running operation, a regenerative operation for outputtingregenerative power by using the kinetic energy of the vehicle which istransmitted from the drive wheel DW.

While a single drive wheel DW is illustrated in FIG. 1 as arepresentative example, a plurality of drive wheels DW are present andmotive power is transmitted from the internal combustion engine 2 or theelectric motor 3 to the plurality of drive wheels DW via a powertrainincluding a differential gear apparatus (not illustrated).

The electric generator 4 is an electric generator configured such that arotating shaft 4 a of the electric generator 4 is driven to rotate byusing the motive power of the internal combustion engine 2, therebybeing able to output generated power. The rotating shaft 4 a of theelectric generator 4 is connected to the output shaft 2 a of theinternal combustion engine 2 via an appropriate powertrain so as torotate in association with the output shaft 2 a of the internalcombustion engine 2. The powertrain in the motive power system 1 in theillustrated example is configured to transmit motive power between theoutput shaft 2 a and the rotating shaft 4 a via two gears 17 and 18, forexample.

In this embodiment, the electric generator 4 further has a function ofan actuator (starter motor) for starting the internal combustion engine2 in addition to the function of an electric generator. That is, poweris supplied to the electric generator 4 to allow the electric generator4 to operate as an electric motor. The motive power of the electricgenerator 4, which serves as an electric motor, is transmitted from therotating shaft 4 a to the output shaft 2 a of the internal combustionengine 2, thereby driving the output shaft 2 a to rotate.

For additional explanation, the powertrain between the internalcombustion engine 2 or the electric motor 3 and the drive wheel DW andthe powertrain between the internal combustion engine 2 and the electricgenerator 4 are not limited to those having the configurationexemplified in FIG. 1 and various configurations are available.

These powertrains may include, for example, components other than gearsfor transmission of motive power, for example, pulleys and belts orsprockets and chains, and may also include gearboxes.

The output shaft 3 a of the electric motor 3 may be coupled coaxiallydirectly to or integrated with any rotating shaft in the powertrainbetween the clutch 11 and the drive wheel DW, for example.

The powertrain between the electric motor 3 and the drive wheel DW orthe powertrain between the internal combustion engine 2 and the electricgenerator 4 may include a clutch.

The motive power system 1 may include, besides the electric generator 4,an actuator for starting the internal combustion engine 2.

The first energy storage device 5 and the second energy storage device 6are energy storage devices chargeable by an external power supplythrough a charging device (not illustrated) included in the vehicle. Thefirst energy storage device 5 and the second energy storage device 6have different characteristics.

Specifically, the first energy storage device 5 is an energy storagedevice having a higher energy density than the second energy storagedevice 6. The energy density is an amount of electrical energy storableper unit weight or unit volume. The first energy storage device 5 may beformed of, for example, a lithium-ion battery.

The second energy storage device 6 is an energy storage device having ahigher power density than the first energy storage device 5. The powerdensity is an amount of electricity that can be output per unit weightor unit volume (an amount of electrical energy per unit time or anamount of charge per unit time). The second energy storage device 6 maybe formed of, for example, a lithium-ion battery, a nickel-hydrogenbattery, or a capacitor.

The first energy storage device 5 with relatively high energy density iscapable of storing a greater amount of electrical energy than the secondenergy storage device 6. The first energy storage device 5 has acharacteristic in which steady discharge with less occurrence of changesin the output of the first energy storage device 5, rather thandischarge with frequent occurrence of changes in the output of the firstenergy storage device 5, suppresses the progression of deterioration ofthe first energy storage device 5.

The first energy storage device 5 further has lower resistance todeterioration due to charging (in particular, charging at high rates)than the second energy storage device 6 (i.e., deterioration of thefirst energy storage device 5 caused by charging is more likely toprogress than that of the second energy storage device 6).

The second energy storage device 6 with relatively high power densityhas lower internal resistance (impedance) than the first energy storagedevice 5, and is thus able to instantaneously output high power. Thesecond energy storage device 6 has a characteristic in which thedischarging or charging of the second energy storage device 6 with thecharge rate being kept within an approximately middle range, rather thanthe discharging or charging of the second energy storage device 6 withthe charge rate being biased toward the high-capacity side or thelow-capacity side, suppresses the progression of deterioration of thesecond energy storage device 6. More specifically, the second energystorage device 6 has a characteristic in which the more the charge rateincreases or decreases toward the high-capacity side or the low-capacityside with respect to the approximately middle range, the more likely theprogression of deterioration of the second energy storage device 6 is tooccur.

The charge rate of each of the energy storage devices 5 and 6 is theratio of the remaining capacity to the full charge capacity. In thefollowing, the charge rate is sometimes referred to as SOC (state ofcharge). In addition, the SOC of the first energy storage device 5 issometimes referred to as the first SOC and the SOC of the second energystorage device 6 as the second SOC.

In this embodiment, the power transmission circuit unit 7 includes aninverter 21 connected to the electric motor 3, an inverter 22 connectedto the electric generator 4, a voltage converter 23 connected to thefirst energy storage device 5, and a voltage converter 24 connected tothe second energy storage device 6.

The inverters 21 and 22 are known circuits each having a switchingelement controlled by a duty signal to convert power from one ofdirect-current (DC) power and alternating-current (AC) power to theother.

The inverter 21 on the electric motor 3 side is capable of performingcontrol to, during the power-running operation of the electric motor 3,convert DC power input from the voltage converter 23 or 24 into AC powerand output the AC power to the electric motor 3, and is also capable ofperforming control to, during the regenerative operation of the electricmotor 3, convert AC power (regenerative power) input from the electricmotor 3 into DC power and output the DC power to the voltage converter23 or 24.

The inverter 22 on the electric generator 4 side is capable ofperforming control to, during the power generation operation of theelectric generator 4, convert AC power (generated power) input from theelectric generator 4 into DC power and output the DC power to thevoltage converter 23 or 24, and is also capable of performing controlto, when the electric generator 4 is driven as an actuator for startingthe internal combustion engine 2, convert DC power input from thevoltage converter 23 or 24 into AC power and output the AC power to theelectric generator 4.

The voltage converters 23 and 24 are known circuits (switching-typeDC/DC converters) each having a switching element controlled by a dutysignal to convert (boost or step down) the voltage of the DC power. Eachof the voltage converters 23 and 24 is capable of variably controllingthe voltage conversion ratio (boosting ratio or step-down ratio), and isalso capable of performing bidirectional power transmission (powertransmission during the discharging of the corresponding one of theenergy storage devices 5 and 6 and power transmission during thecharging of the corresponding one of the energy storage devices 5 and6).

The control device 8 is constituted by an electronic circuit unitincluding a central processing unit (CPU), a random access memory (RAM),a read-only memory (ROM), an interface circuit, and so on. The controldevice 8 may be constituted by a plurality of electronic circuit unitsthat are capable of communicating with each other.

The control device 8 includes, as functions implemented by a hardwareconfiguration to be mounted therein or by a program (softwareconfiguration) to be installed therein, an internal combustion engineoperation controller 31, a power transmission controller 32, a clutchcontroller 33, and a brake controller 34. The internal combustion engineoperation controller 31 controls the operation of the internalcombustion engine 2. The power transmission controller 32 controls thepower transmission circuit unit 7 (and therefore controls the operationof the electric motor 3 and the electric generator 4). The clutchcontroller 33 controls switching between operating states of the clutch11. The brake controller 34 controls a brake device (not illustrated) ofthe vehicle.

The control device 8 receives input of various sensing data asinformation necessary to implement the functions described above. Thesensing data includes, for example, data indicating the amount ofoperation of the accelerator pedal of the vehicle, the amount ofoperation of the brake pedal, the vehicle speed, the rotational speed ofthe output shaft 2 a of the internal combustion engine 2, the rotationalspeed of the output shaft 3 a of the electric motor 3, the rotationalspeed of the rotating shaft 4 a of the electric generator 4, and therespective detected values of the first SOC and the second SOC.

The control device 8 may include a function of an SOC detector thatdetects (estimates) the first SOC and the second SOC. In this case, thecontrol device 8 receives input of sensing data for estimating the firstSOC and the second SOC (for example, data indicating detected values ofthe voltage, current, temperature, and the like of the energy storagedevices 5 and 6) instead of sensing data indicating the respectivedetected values of the first SOC and the second SOC.

A specific description will now be given of a control process for thecontrol device 8.

Overview of Control Process for Control Device 8

First, a description will be given of an overview of a control processexecuted by the control device 8. The control process executed by thecontrol device 8 is broadly categorized into two types: a controlprocess for a charge-depleting (CD) mode and a control process for acharge-sustaining (CS) mode. The CD mode and the CS mode representoperation types of the motive power system 1 when the vehicle istraveling.

In this embodiment, the CD mode is a mode in which the motive power ofthe electric motor 3, out of the internal combustion engine 2 and theelectric motor 3, is usable as motive power for driving the drive wheelDW (as motive power for propelling the vehicle).

In the CD mode in this embodiment, the stored energy of the first energystorage device 5, out of the first energy storage device 5 and thesecond energy storage device 6, is used as the primary power sourceenergy for the electric motor 3 to perform the power-running operationof the electric motor 3.

In the CD mode in this embodiment, additionally, the internal combustionengine 2 remains at rest (the operation of the internal combustionengine 2 is disabled).

In this embodiment, in contrast, the CS mode is a mode in which themotive power of the internal combustion engine 2 and the motive power ofthe electric motor 3 are usable as motive power for driving the drivewheel DW. More specifically, the CS mode is a mode in which the motivepower of the internal combustion engine 2 is usable as primary motivepower for driving the drive wheel DW and the motive power of theelectric motor 3 is usable as auxiliary motive power for driving thedrive wheel DW.

The CS mode in this embodiment is divided into a first CS mode and asecond CS mode. In the first CS mode, the power in the second energystorage device 6, out of the first energy storage device 5 and thesecond energy storage device 6, is used as primary power source energyfor the power-running operation of the electric motor 3 and the power inthe second energy storage device 6 is used to charge (or is transferredto) the first energy storage device 5, if necessary, to graduallyrestore the SOC of the first energy storage device 5 (i.e., the firstSOC). In the second CS mode, the power in the first energy storagedevice 5, out of the first energy storage device 5 and the second energystorage device 6, is used as primary power source energy for thepower-running operation of the electric motor 3 and the generated powerof the electric generator 4 is used to charge the second energy storagedevice 6 to restore the SOC of the second energy storage device 6 (i.e.,the second SOC).

The control process in the first CS mode and the control process in thesecond CS mode are alternately executed so as to place the total chargeand discharge of the first energy storage device 5 and the second energystorage device 6 in balance as appropriate. As a result of repeating thecontrol process in the first CS mode and the control process in thesecond CS mode or as a result of plug-in charging with an externalelectric power system, the SOC of the first energy storage device 5 isrestored to some extent. Then, the mode of the control process isreturned from the CS mode to the CD mode.

A pattern indicating how the respective stored energies of the firstenergy storage device 5 and the second energy storage device 6 are usedin this embodiment will now be described with reference to FIG. 2.

In this embodiment, as depicted in a left percentage bar chart in FIG.2, a capacity (stored energy) of the range less than or equal to B1a (%)out of the full charge capacity (100% SOC) of the first energy storagedevice 5 is allocated as a capacity usable for power supply to theelectric motor 3. B1a (%) is set to represent a charge rate slightlyless than 100% with consideration given to a detection error of thefirst SOC, an error of charge control, or the like.

A capacity of the range of B1a (%) to B1b (%) is allocated as a capacityused for power supply to the electric motor 3 in the CD mode, and therange less than or equal to B1b (%) is allocated as a range thatincludes a capacity usable for power supply to the electric motor 3 inthe CS mode in an auxiliary manner. B1b (%) is set to represent an SOCclose to 0%.

The range less than or equal to B1b (%) includes, in addition to thecapacity usable for power supply to the electric motor 3 in the CS mode,margins that take into account a detection error of the first SOC or thelike.

In this manner, a range that occupies a large proportion (the range ofB1a (%) to B1b (%)) of the full charge capacity of the first energystorage device 5 is allocated as a capacity used for power supply to theelectric motor 3 in the CD mode.

In this embodiment, as depicted in a right percentage bar chart in FIG.2, a capacity of the range of B2a (%) to B2b (%) out of the full chargecapacity (100% SOC) of the second energy storage device 6 is allocatedas a dedicated capacity usable for power supply to the electric motor 3in the CD mode, and a capacity of the range of B2b (%) to B2c (%) isallocated as a capacity usable for power supply to the electric motor 3in the CS mode.

In this embodiment, part of the capacity of the range of B2b (%) to B2c(%) is also usable in the CD mode. Note that the capacity of the rangeof B2b (%) to B2c (%) is a capacity which is temporarily usable in theCD mode and which can basically be replenished, after part of thecapacity has been used for power supply to the electric motor 3, by thefirst energy storage device 5 by the amount used.

To minimize the progression of deterioration of the second energystorage device 6, it is preferable to discharge or charge the secondenergy storage device 6 when the second SOC is an SOC near anintermediate value. Accordingly, B2b (%) is set to approximately anintermediate SOC, B2a (%) is set to a value larger than B2b (%) to suchan extent that B2a (%) is not too close to 100%, and B2c (%) is set to avalue smaller than B2b (%) to such an extent that B2c (%) is not tooclose to 0%.

The range less than or equal to B2c (%) is allocated as a range thatincludes power for starting the internal combustion engine 2 (powerusable for power supply to the electric generator 4 serving as a starteractuator.

In this embodiment, when the internal combustion engine 2 is started,the second energy storage device 6 supplies power to the electricgenerator 4 and the power in the first energy storage device 5 is notused for power supply to the electric generator 4. This eliminates theneed for the first energy storage device 5 to reserve power for startingthe internal combustion engine 2.

This can increase the SOC range of the first energy storage device 5which is allocated as a capacity range for power supply to the electricmotor 3 in the CD mode. That is, in the CD mode in which fuelconsumption of the internal combustion engine 2 does not occur or issuppressed, the drivable range of the vehicle is increased and theenvironmental performance of the motive power system 1 is improved.Additionally, instantaneous power supply to the starter actuator (inthis embodiment, the electric generator 4), which is required to startthe internal combustion engine 2, is undertaken by the second energystorage device 6. This can favorably suppress the progression ofdeterioration of the first energy storage device 5.

As illustrated in FIG. 2, in the CD mode, the SOC range (of B1a (%) toB1b (%)) of the first energy storage device 5 usable for power supply tothe electric motor 3 is larger than the SOC range (of B2a (%) to B2b(%)) of the second energy storage device 6 usable for power supply tothe electric motor 3.

Thus, in the CD mode, the power in the first energy storage device 5 canbe primarily used to perform the power-running operation of the electricmotor 3. In addition, the power in the second energy storage device 6can also be used in an auxiliary manner, if necessary, to perform thepower-running operation of the electric motor 3.

In particular, there is no need for the first energy storage device 5 toreserve power for starting the internal combustion engine 2. This makesit possible to maximize the SOC range (of B1a (%) to B1b (%)) usable forpower supply to the electric motor 3 in the CD mode.

As a result, in the CD mode in which only the motive power of theelectric motor 3 is used to propel the vehicle, the period during whichpower can be continuously supplied to the electric motor 3, andtherefore the drivable range of the vehicle in the CD mode in which fuelconsumption of the internal combustion engine 2 does not occur or issuppressed, can be maximized and the environmental performance of thevehicle can be improved.

In the CS mode, in contrast, as illustrated in FIG. 2, the SOC range (ofB2b (%) to B2c (%)) of the second energy storage device 6 usable forpower supply to the electric motor 3 is larger than the SOC range (partof the range less than or equal to B1b (%)) of the first energy storagedevice 5 usable for power supply to the electric motor 3.

Thus, in the CS mode, motive power that is supplementary to the motivepower of the internal combustion engine 2 to drive the drive wheel DW(propel the vehicle) can be generated quickly (with high responsivity)primarily by supplying power from the high-power second energy storagedevice 6 to the electric motor 3.

Accordingly, when the motive power system 1 outputs a high driving forceto the drive wheel DW, the electric motor 3 outputs auxiliary motivepower by power supply from the second energy storage device 6. Thisenables not only suppression of excessive fuel consumption of theinternal combustion engine 2 but also reduction in the displacement ofthe internal combustion engine 2.

In addition, since the second energy storage device 6 has a higher powerdensity than the first energy storage device 5, the resistance of thesecond energy storage device 6 to charge or discharge for which highresponsivity is required is superior to that of the first energy storagedevice 5. This can further suppress deterioration of the first energystorage device 5.

Main Routine Process

On the basis of the foregoing, a detailed description will be given ofthe control process for the control device 8. The control device 8sequentially executes a main routine process illustrated in a flowchartin FIG. 3 in a predetermined control process cycle when the vehicle isstarted.

In STEP1, the control device 8 acquires the current mode of the controlprocess, a detected value of the SOC of the first energy storage device5 (i.e., the first SOC), and a detected value of the SOC of the secondenergy storage device 6 (i.e., the second SOC).

If the first energy storage device 5 is charged up to the fully-chargedlevel (or up to the an SOC greater than or equal to a CS→CD switchingthreshold B1_mc2 described below) while the vehicle is at rest beforethe vehicle is started, the initial mode of the control process afterthe start of the vehicle is the CD mode. If the first energy storagedevice 5 is not charged while the vehicle is at rest before the vehicleis started, the initial mode of the control process after the start ofthe vehicle is the same mode as the mode set at the end of the previousdriving operation of the vehicle.

Then, in STEP2, the control device 8 determines whether or not thecurrent mode of the control process is the CD mode. If the determinationresult of STEP2 is affirmative, in STEP3, the control device 8 furtherdetermines whether or not the detected value of the first SOC is greaterthan or equal to a predetermined mode switching threshold B1_mc1. Themode switching threshold B1_mc1 is a threshold that defines whether ornot to perform switching from the CD mode to the CS mode, and ishereinafter referred to as the CD→CS switching threshold B1_mc1. In thisembodiment, the CD→CS switching threshold B1_mc1 is set to B1b (%)illustrated in FIG. 2.

If the determination result of STEP3 is affirmative, in STEP4, thecontrol device 8 selects the CD mode as the mode of the control processand executes a control process for the CD mode (described in detailbelow). In this case, the control process for the CD mode iscontinuously executed.

If the determination result of STEP3 is negative, then, in STEP5, thecontrol device 8 determines whether or not the detected value of thesecond SOC is greater than or equal to a mode switching threshold (afirst switching threshold) B2_mc1. The mode switching threshold B2_mc1is a threshold that defines whether or not to perform switching from thefirst CS mode to the second CS mode, and is hereinafter referred to asthe CS1→CS2 switching threshold B2_mc1. In this embodiment, the CS1→CS2switching threshold B2_mc1 is set to B2c (%) illustrated in FIG. 2.

If the determination result of STEP5 is affirmative, in STEP6, thecontrol device 8 selects the first CS mode as the mode of the controlprocess and executes a control process for the first CS mode (describedin detail below). Thus, the mode of the control process is switched fromthe CD mode to the first CS mode.

If the determination result of STEP5 is negative, in STEP7, the controldevice 8 executes a power generation control process for performing apower generation operation of the electric generator 4.

In the power generation control process, the control device 8 instructsthe internal combustion engine operation controller 31 and the powertransmission controller 32 to perform a power generation operation ofthe electric generator 4.

In this case, the internal combustion engine operation controller 31controls the internal combustion engine 2 to output, from the internalcombustion engine 2, motive power to which motive power for driving theelectric generator 4 is added. The power transmission controller 32controls the power transmission circuit unit 7 to preferentially chargethe second energy storage device 6, out of the first energy storagedevice 5 and the second energy storage device 6, with generated powerproduced by the electric generator 4 which is supplied with the motivepower of the internal combustion engine 2. Specifically, the powertransmission controller 32 controls the voltage converter 24 and theinverter 22 of the power transmission circuit unit 7 to charge only thesecond energy storage device 6 with the generated power, except for thecase where the detected value of the first SOC is smaller than apredetermined value (e.g., a threshold (a first change rate threshold)B1_th1 described below (see FIG. 11)).

If the detected value of the first SOC is smaller than the predeterminedvalue and while power supply to the electric motor 3 is halted, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 22 of the power transmission circuit unit 7 tocharge both the first energy storage device 5 and the second energystorage device 6 with the generated power. In this case, the amount ofgenerated power used to charge the first energy storage device 5 islimited to an amount of charging power at low rates (low speeds) tosuppress the progression of deterioration of the first energy storagedevice 5.

Thus, the second energy storage device 6 is preferentially charged withthe generated power. If the charge rate of the first energy storagedevice 5 is low, the first energy storage device 5 is appropriatelycharged with part of the generated power at a low rate.

Note that the internal combustion engine 2 is not always in operationand has not started its operation when the determination result of STEP5is negative. In this case, the control device 8 instructs the internalcombustion engine operation controller 31 and the power transmissioncontroller 32 to perform a power generation operation of the electricgenerator 4 after the internal combustion engine 2 has been started.

In the process for starting the internal combustion engine 2, the powertransmission circuit unit 7 controls the voltage converter 24 on thesecond energy storage device 6 side and the inverter 22 on the electricgenerator 4 side to supply power from the second energy storage device 6to the electric generator 4 (and to therefore cause the electricgenerator 4 to operate as a starter motor). This allows the output shaft2 a of the internal combustion engine 2 to be driven to rotate by themotive power of the electric generator 4 serving as a starter actuator(starter motor). In this embodiment, therefore, the second energystorage device 6 supplies power to the electric generator 4 (startermotor) when the internal combustion engine 2 is started.

Since instantaneous power supply to the starter actuator (the electricgenerator 4), which is required to start the internal combustion engine2, is undertaken by the second energy storage device 6, the progressionof deterioration of the first energy storage device 5 can be favorablysuppressed.

Then, the internal combustion engine operation controller 31 suppliesfuel to the internal combustion engine 2 in synchronization with therotation of the output shaft 2 a of the internal combustion engine 2 tostart the combustion operation of the internal combustion engine 2.Thereafter, the internal combustion engine operation controller 31 andthe power transmission controller 32 execute the control processdescribed above for performing a power generation operation of theelectric generator 4, thereby starting the power generation operation ofthe electric generator 4 and the charging of the second energy storagedevice 6 with the generated power.

After the power generation control process in STEP7, in STEP8, thecontrol device 8 selects the second CS mode as the mode of the controlprocess and executes a control process for the second CS mode (describedin detail below). Thus, the mode of the control process is switched fromthe CD mode to the second CS mode.

For additional explanation, in the second CS mode, the charging of thesecond energy storage device 6 through the power generation operation ofthe electric generator 4 is interrupted during the regenerativeoperation of the electric motor 3. In this case, the inverter 22 of thepower transmission circuit unit 7 is controlled so that the energizationof the inverter 22 is interrupted. Note that charging of the secondenergy storage device 6 with the regenerative power of the electricmotor 3 and charging of the second energy storage device 6 with thegenerated power of the electric generator 4 may be performed inparallel.

If the determination result of STEP2 is negative, then, in STEP9, thecontrol device 8 determines whether or not the current mode of thecontrol process is the first CS mode.

If the determination result of STEP9 is affirmative, in STEP10, thecontrol device 8 further determines whether or not the detected value ofthe first SOC is greater than or equal to a predetermined mode switchingthreshold B1_mc2. The mode switching threshold B1_mc2 is a thresholdthat defines whether or not to perform switching from the CS mode to theCD mode, and is hereinafter referred to as the CS→CD switching thresholdB1_mc2. In this embodiment, the CS→CD switching threshold B1_mc2 is setto a value higher than the mode switching threshold B1_mc1 in STEP3 toprovide hysteresis for switching between the first CS mode and thesecond CS mode, and is set to, for example, a value between B1b (%) andB1a (%) illustrated in FIG. 2.

If the determination result of STEP10 is affirmative, in STEP4, thecontrol device 8 selects the CD mode as the mode of the control processand executes the control process for the CD mode. Thus, the mode of thecontrol process is switched from the CS mode (first CS mode) to the CDmode.

If the determination result of STEP10 is negative, the control device 8executes the process from STEP5 described above. If the determinationresult of STEP5 is affirmative, the control process for the first CSmode is continuously executed. If the determination result of STEP5 isnegative, the mode of the control process is switched from the first CSmode to the second CS mode.

If the determination result of STEP9 is negative, in STEP11, the controldevice 8 further determines whether or not the detected value of thesecond SOC is greater than or equal to a predetermined mode switchingthreshold (a second switching threshold) B2_mc2. The mode switchingthreshold B2_mc2 is a threshold that defines whether or not to performswitching from the second CS mode to the first CS mode, and ishereinafter referred to as the CS2→CS1 switching threshold B2_mc2. Inthis embodiment, the CS2→CS1 switching threshold B2_mc2 is set to B2b(%) (>the CS1→CS2 switching threshold B2_mc1) illustrated in FIG. 2.

If the determination result of STEP11 is affirmative, in STEP6, thecontrol device 8 selects the first CS mode as the mode of the controlprocess and executes the control process for the first CS mode. Thus,the mode of the control process is switched from the second CS mode tothe first CS mode.

If the determination result of STEP11 is negative, the control device 8executes the process from STEP7 described above. In this case, throughthe processing of STEP7 and STEP8, the power generation operation of theelectric generator 4 is continuously executed and the control process inthe second CS mode is also continuously executed.

As described above, switching between the CD mode and the CS mode isbased on the first SOC and switching between the first CS mode and thesecond CS mode is based on the second SOC.

Control Process for CD Mode

Next, the control process for the CD mode in STEP4 will be described indetail.

The control device 8 determines a required driving force (requiredpropulsion force) or required braking force of the entire vehicle inaccordance with the detected value of the amount of operation of theaccelerator pedal of the vehicle, the detected value of the amount ofoperation of the brake pedal of the vehicle, the detected value of thevehicle speed, and so on, and also determines the respective targetoperating states of the internal combustion engine 2, the electric motor3, the electric generator 4, the clutch 11, and the brake device.

In the CD mode, the control device 8 maintains the internal combustionengine 2 and the electric generator 4 at rest and also maintains theclutch 11 in the disconnected state.

In a situation where the required driving force of the entire vehicle isnot zero (this situation is hereinafter referred to as the vehicledriving request state), the control device 8 determines a requiredoutput DM_dmd of the electric motor 3 so as to realize the requireddriving force by using the motive power of the electric motor 3.

Then, as described in detail below, the control device 8 causes thepower transmission controller 32 to control the inverter 21 on theelectric motor 3 side and the voltage converters 23 and 24 of the powertransmission circuit unit 7 to supply power from either or both of thefirst energy storage device 5 and the second energy storage device 6 tothe electric motor 3 in accordance with a pre-created map illustrated inFIG. 4 on the basis of the required output DM_dmd and the detected valueof the SOC of the second energy storage device 6 (i.e., the second SOC).

Examples of the required output DM_dmd of the electric motor 3 mayinclude a request value of the amount of electrical energy to besupplied to the electric motor 3 per unit time (in other words, arequested power value), a driving force to be output from the electricmotor 3, and a request value of the amount of mechanical output energyper unit time, and a request value of the current which is to flowthrough the electric motor 3 to output motive power (an output torque)that can satisfy the required driving force of the vehicle from theelectric motor 3.

In this embodiment, the request value of the amount of electrical energyto be supplied to the electric motor 3 per unit time is used as anexample of the required output DM_dmd of the electric motor 3.

In a situation where the required braking force of the entire vehicle isnot zero (this situation is hereinafter referred to as the vehiclebraking request state), the control device 8 determines respectiveshares of the required braking force for the electric motor 3 and thebrake device. In this case, the control device 8 determines therespective shares for the electric motor 3 and the brake device on thebasis of the magnitude of the required braking force, the detected valueof the second SOC, and so on so as to basically maximize the share ofthe required braking force for the electric motor 3.

Then, the control device 8 causes the brake controller 34 to control thebrake device in accordance with the share of the required braking forcefor the brake device.

Further, the control device 8 determines a required amount ofregeneration G_dmd of the electric motor 3 so that the share of therequired braking force for the electric motor 3 is satisfied by aregenerative braking force generated through the regenerative operationof the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to chargeeither or both of the first energy storage device 5 and the secondenergy storage device 6 with the regenerative power output from theelectric motor 3 in accordance with a pre-created map illustrated inFIG. 9 on the basis of the required amount of regeneration G_dmd and thedetected value of the SOC of the second energy storage device 6 (i.e.,the second SOC). In this case, in this embodiment, the primary energystorage device to be charged with the regenerative power in the CD modeis the second energy storage device 6.

Examples of the required amount of regeneration G_dmd of the electricmotor 3 may include, as the share of the required braking force of theentire vehicle that is taken on by the electric motor 3, a request valueof the regenerative braking force generated by the electric motor 3performing a regenerative operation, a request value of the regenerativepower generated by the electric motor 3 performing a regenerativeoperation (the amount of electrical energy generated per unit time), anda request value of the current which is to flow through the electricmotor 3.

In this embodiment, the request value of the regenerative power is usedas an example of the required amount of regeneration G_dmd of theelectric motor 3.

Control Process During Power-Running Operation in CD Mode

A control process executed by the power transmission controller 32during the power-running operation of the electric motor 3 in the CDmode will be described in detail hereinafter with reference to FIGS. 4to 8.

FIG. 4 illustrates a map depicting how the output demand for the amountof electricity to be supplied (the amount of power supplied) to theelectric motor 3 is shared by the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required outputDM_dmd of the electric motor 3 and the second SOC.

In FIG. 4, diagonally hatched areas represent areas where all or part ofthe amount of power supplied to the electric motor 3 is taken on by thefirst energy storage device 5 and a shaded area represents an area whereall or part of the amount of power supplied to the electric motor 3 istaken on by the second energy storage device 6.

More specifically, the lower diagonally hatched area represents an areawhere all the amount of power supplied to the electric motor 3 is takenon only by the first energy storage device 5 and the shaded area or theupper diagonally hatched area represents an area where the amount ofpower supplied to the electric motor 3 is taken on by both the firstenergy storage device 5 and the second energy storage device 6.

On the map illustrated in FIG. 4, DM_max1 is a maximum value of therequired output DM_dmd in the CD mode. The maximum value DM_max1 is aconstant value when the second SOC is an SOC greater than or equal to apredetermined value B2e. When the second SOC is smaller than the valueB2e, the maximum value DM_max1 decreases in accordance with the decreasein the second SOC.

In the control process during the power-running operation of theelectric motor 3 in the CD mode, as illustrated in FIG. 4, the sharesfor the respective outputs of the first energy storage device 5 and thesecond energy storage device 6 are identified for the cases where thevalue of the second SOC falls within a high-SOC area(high-remaining-capacity area), a medium-SOC area(medium-remaining-capacity area), and a low-SOC area(low-remaining-capacity area) in the usable area of the second energystorage device 6 (the range of B2a to B2c illustrated in FIG. 2). Thehigh-SOC area is an area where SOC≥B2_th1 is satisfied. The medium-SOCarea is an area where B2_th1>SOC≥B2_th2 is satisfied. The low-SOC areais an area where B2_th2>SOC is satisfied.

On the map illustrated in FIG. 4, the thresholds B2_th1 and B2_th2 bywhich the second SOC is separated are thresholds (fixed values)determined in advance for the CD mode. The thresholds B2_th1 and B2_th2are set in advance experimentally, for example, so that the medium-SOCarea whose range is determined by the thresholds B2_th1 and B2_th2 is anSOC area within which the actual value of the second SOC preferablyfalls to minimize the progression of deterioration of the second energystorage device 6. Accordingly, the medium-SOC area is an area withinwhich the progression of deterioration of the second energy storagedevice 6 can be favorably suppressed when the second energy storagedevice 6 is charged or discharged with the actual value of the secondSOC being kept within the medium-SOC area as much as possible.

In this embodiment, the control process in the CD mode is performed withthe second SOC being kept within the medium-SOC as much as possible tosuppress the progression of deterioration of the second energy storagedevice 6.

In this embodiment, the threshold B2_th1, which is the lower limit ofthe high-SOC area, matches B2b (%) illustrated in FIG. 2. Accordingly,within the capacity of the second energy storage device 6, a capacity(stored energy) in the range of the high-SOC area is a dedicatedcapacity usable in the CD mode.

A control process for the power transmission controller 32 during thepower-running operation of the electric motor 3 in the CD mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 4 in accordance with a flowchart illustratedin FIGS. 5 to 7.

In STEP21, the power transmission controller 32 acquires the requiredoutput DM_dmd and a detected value of the second SOC. Then, in STEP22,the power transmission controller 32 determines whether or not thedetected value of the second SOC acquired in STEP21 is greater than orequal to the threshold B2_th1, which is the upper limit of themedium-SOC area.

The determination result of STEP22 is affirmative in the situation wherethe detected value of the second SOC falls within the high-SOC area. Inthis case, then, in STEP23, the power transmission controller 32determines whether or not the required output DM_dmd is less than orequal to a predetermined threshold DM_th1.

In this embodiment, the threshold DM_th1 is a threshold used for boththe medium-SOC area and the high-SOC area. As illustrated in FIG. 4, thethreshold DM_th1 is a predetermined constant value (fixed value) atvalues greater than or equal to a predetermined value B2d in themedium-SOC area. The constant value is a value determined so that theamount of power supplied corresponding to this value is sufficientlysmaller than the allowable upper limit on the amount of power suppliedto be output from the first energy storage device 5.

In a portion of the medium-SOC area smaller than the value B2d, thethreshold DM_th1 is set so that the amount of power suppliedcorresponding to the threshold DM_th1 matches a base amount of powersupplied P1_base described below (and consequently changes in accordancewith the second SOC). In this case, the threshold DM_th1 increases asthe second SOC decreases.

For additional explanation, the amount of power supplied correspondingto a certain threshold for the required output DM_dmd refers to theamount of electricity to be supplied to the electric motor 3 when therequired output DM_dmd matches this threshold.

The determination result of STEP23 is affirmative for the lowerdiagonally hatched area in the high-SOC area illustrated in FIG. 4. Inthis case, in STEP24, the power transmission controller 32 controls thevoltage converter 23 and the inverter 21 of the power transmissioncircuit unit 7 so that an output P1 of the first energy storage device 5matches the amount of power supplied corresponding to the requiredoutput DM_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block discharge from thesecond energy storage device 6.

The output P1 of the first energy storage device 5 is specifically anamount of electricity output (an amount of power discharged) from thefirst energy storage device 5, and an output P2 of the second energystorage device 6 (described below) is specifically an amount ofelectricity output (an amount of power discharged) from the secondenergy storage device 6. The amount of power supplied corresponding tothe required output DM_dmd refers to the amount of electricity to besupplied to the electric motor 3 to realize the required output DM_dmd.

If the determination result of STEP23 is negative, then, in STEP25, thepower transmission controller 32 determines whether or not the requiredoutput DM_dmd is less than or equal to a predetermined threshold DM_th2.

In this embodiment, similarly to the threshold DM_th1 in STEP23, thethreshold DM_th2 is a threshold used for both the medium-SOC area andthe high-SOC area. The threshold DM_th2 is set to a threshold largerthan the threshold DM_th1 by a predetermined amount.

In this case, the threshold DM_th2 may be set so that, for example, theamount of power supplied which is equivalent to the difference betweenthe threshold DM_th2 and the threshold DM_th1 (=DM_th2−DM_th1) is equalto the allowable upper limit on the amount of power supplied for thesecond energy storage device 6 in the CD mode or is equal to an amountof power supplied which is close to the allowable upper limit.

The determination result of STEP25 is affirmative for the shaded area inthe high-SOC area illustrated in FIG. 4. In this case, in STEP26, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 21 of the power transmission circuit unit 7 so thatthe output P1 of the first energy storage device 5 matches the amount ofpower supplied corresponding to the threshold DM_th1 and so that theoutput P2 of the second energy storage device 6 matches the amount ofpower supplied which is obtained by subtracting the output P1 of thefirst energy storage device 5 from the amount of power suppliedcorresponding to the required output DM_dmd.

On the other hand, the determination result of STEP25 is negative forthe upper diagonally hatched area in the high-SOC area illustrated inFIG. 4. In this situation, in STEP27, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the amount of power suppliedcorresponding to the difference between the thresholds DM_th1 and DM_th2(=DM_th2−DM_th1) and so that the output P1 of the first energy storagedevice 5 matches the amount of power supplied which is obtained bysubtracting the output P2 of the second energy storage device 6 from theamount of power supplied corresponding to the required output DM_dmd.

If the determination result of STEP22 is negative, then, in STEP28, thepower transmission controller 32 further determines whether or not thedetected value of the second SOC is greater than or equal to thethreshold B2_th2, which is the lower limit of the medium-SOC area.

The determination result of STEP28 is affirmative in the situation wherethe detected value of the second SOC falls within the medium-SOC area.In this case, then, in STEP29 illustrated in FIG. 6, the powertransmission controller 32 determines the base amount of power suppliedP1_base, which is a base value of the output P1 of the first energystorage device 5, in accordance with the detected value of the secondSOC.

The base amount of power supplied P1_base is a lower limit on the amountof electricity that is output from the first energy storage device 5regardless of the required output DM_dmd of the electric motor 3 whenthe detected value of the second SOC falls within the medium-SOC area orthe low-SOC area. That is, in this embodiment, when the detected valueof the second SOC falls within the medium-SOC area or the low-SOC area,the power transmission circuit unit 7 is controlled so that the baseamount of power supplied P1_base or a larger amount of power supplied isoutput from the first energy storage device 5 regardless of the requiredoutput DM_dmd.

The base amount of power supplied P1_base is determined from thedetected value of the second SOC on the basis of a pre-created map or acalculation formula so that the base amount of power supplied P1_basechanges in accordance with the second SOC in a pattern indicated by abroken line illustrated in FIG. 4, for example. In this case, the baseamount of power supplied P1_base is determined to successively increasefrom zero to a maximum value P1b within the medium-SOC area inaccordance with the decrease in the second SOC and to be kept constantat the maximum value P1b within the low-SOC area. The maximum value P1bis a value larger than the amount of power supplied corresponding to thethreshold DM_th1 when the second SOC is greater than or equal to thepredetermined value B2d in the medium-SOC area.

After determining the base amount of power supplied P1_base in the waydescribed above, then, in STEP30, the power transmission controller 32determines whether or not the amount of power supplied corresponding tothe required output DM_dmd is smaller than the base amount of powersupplied P1_base.

The determination result of STEP30 is affirmative for an area below thebroken line within the lower diagonally hatched area in the medium-SOCarea illustrated in FIG. 4. In this situation, in STEP31, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theoutput P1 of the first energy storage device 5 matches the base amountof power supplied P1_base and so that an input Pc2 of the second energystorage device 6, that is, the amount of charging power, matches theamount of power supplied which is obtained by subtracting the amount ofpower supplied corresponding to the required output DM_dmd from the baseamount of power supplied P1_base.

If the determination result of STEP30 is negative, in STEP32, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to the threshold DM_th1.

The determination result of STEP32 is affirmative for an area obtainedby removing the area below the broken line from the lower diagonallyhatched area in the medium-SOC area illustrated in FIG. 4 (specifically,an area obtained by combining the area along the broken line and an areaabove the broken line).

In this situation, in STEP33, as in STEP24, the power transmissioncontroller 32 controls the voltage converter 23 and the inverter 21 ofthe power transmission circuit unit 7 so that the output P1 of the firstenergy storage device 5 matches the amount of power suppliedcorresponding to the required output DM_dmd. In this case, the voltageconverter 24 on the second energy storage device 6 side is controlled toblock discharge from the second energy storage device 6.

If the determination result of STEP32 is negative, in STEP34, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to the threshold DM_th2.

The determination result of STEP34 is affirmative for the shaded area inthe medium-SOC area illustrated in FIG. 4. In this situation, in STEP35,as in STEP26, the power transmission controller 32 controls the voltageconverters 23 and 24 and the inverter 21 of the power transmissioncircuit unit 7 so that the output P1 of the first energy storage device5 matches the amount of power supplied corresponding to the thresholdDM_th1 and so that the output P2 of the second energy storage device 6matches the amount of power supplied which is obtained by subtractingthe output P1 of the first energy storage device 5 from the amount ofpower supplied corresponding to the required output DM_dmd.

On the other hand, the determination result of STEP34 is negative forthe upper diagonally hatched area in the medium-SOC area illustrated inFIG. 4. In this situation, in STEP36, as in STEP27, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theoutput P2 of the second energy storage device 6 matches the amount ofpower supplied corresponding to the difference between the thresholdsDM_th1 and DM_th2 (=DM_th2−DM_th1) and so that the output P1 of thefirst energy storage device 5 matches the amount of power supplied whichis obtained by subtracting the output P2 of the second energy storagedevice 6 from the amount of power supplied corresponding to the requiredoutput DM_dmd.

Then, the determination result of STEP28 is negative in the situationwhere the detected value of the second SOC falls within the low-SOCarea. In this case, then, in STEP37 illustrated in FIG. 7, the powertransmission controller 32 determines the base amount of power suppliedP1_base by using the same or substantially the same process as that inSTEP29. Then, in STEP38, the power transmission controller 32 furtherdetermines whether or not the amount of power supplied corresponding tothe required output DM_dmd is smaller than the base amount of powersupplied P1_base.

The determination result of STEP38 is affirmative for an area below thebroken line within the lower diagonally hatched area in the low-SOC areaillustrated in FIG. 4. In this situation, in STEP39, as in STEP31, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 21 of the power transmission circuit unit 7 so thatthe output P1 of the first energy storage device 5 matches the baseamount of power supplied P1_base and so that the input Pc2 of the secondenergy storage device 6, that is, the amount of charging power, matchesthe amount of power supplied which is obtained by subtracting the amountof power supplied corresponding to the required output DM_dmd from thebase amount of power supplied P1_base.

If the determination result of STEP38 is negative, in STEP40, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to a predeterminedthreshold DM_th3.

The determination result of STEP40 is affirmative for an area obtainedby removing the area below the broken line from the diagonally hatchedarea in the low-SOC area illustrated in FIG. 4 (specifically, an areaobtained by combining the area along the broken line and an area abovethe broken line).

In this situation, in STEP41, as in STEP24 or STEP33, the powertransmission controller 32 controls the voltage converter 23 and theinverter 21 of the power transmission circuit unit 7 so that the outputP1 of the first energy storage device 5 matches the amount of powersupplied corresponding to the required output DM_dmd. In this case, thevoltage converter 24 on the second energy storage device 6 side iscontrolled to block discharge from the second energy storage device 6.

On the other hand, the determination result of STEP40 is negative forthe shaded area in the low-SOC area illustrated in FIG. 4. In thissituation, in STEP42, the power transmission controller 32 controls thevoltage converters 23 and 24 and the inverter 21 of the powertransmission circuit unit 7 so that the output P1 of the first energystorage device 5 matches the amount of power supplied corresponding tothe threshold DM_th3 and so that the output P2 of the second energystorage device 6 matches the amount of power supplied which is obtainedby subtracting the output P1 of the first energy storage device 5 fromthe amount of power supplied corresponding to the required outputDM_dmd.

The control process during the power-running operation of the electricmotor 3 in the CD mode is executed in the way described above. In thiscontrol process, when the detected value of the second SOC falls withinthe high-SOC area, power is supplied from the second energy storagedevice 6 to the electric motor 3 in a range where the required outputDM_dmd is less than or equal to the threshold DM_th2 (a comparativelycommonly used range), except for the case where the required outputDM_dmd is less than or equal to the comparatively small thresholdDM_th1. In the high-SOC area, furthermore, the second energy storagedevice 6 is not charged with power supplied by the first energy storagedevice 5.

This can make the second SOC close to the medium-SOC area where theprogression of deterioration of the second energy storage device 6 isfavorably suppressed.

When the detected value of the second SOC falls within the medium-SOCarea or the low-SOC area, if the amount of power supplied correspondingto the required output DM_dmd is less than or equal to the base amountof power supplied P1_base, the output P1 of the first energy storagedevice 5 is retained at the base amount of power supplied P1_base, whichis set in accordance with the detected value of the second SOC.

If the amount of power supplied corresponding to the required outputDM_dmd is smaller than the base amount of power supplied P1_base, theamount of power supplied corresponding to the required output DM_dmd,which is a portion of the base amount of power supplied P1_base, issupplied from only the first energy storage device 5 to the electricmotor 3 and, also, the second energy storage device 6 is charged withthe amount of power supplied which is obtained by subtracting the amountof power supplied corresponding to the required output DM_dmd from thebase amount of power supplied P1_base.

In addition, as the second SOC decreases, the range of the requiredoutput DM_dmd in which the second energy storage device 6 is chargedwith power supplied from the first energy storage device 5 is increasedand the amount of charging power of the second energy storage device 6is more likely to increase.

As a result, when the second SOC falls within the medium-SOC area or thelow-SOC area, if power is supplied from the second energy storage device6 to the electric motor 3, then, the second energy storage device 6 canbe basically replenished by being charged with power supplied from thefirst energy storage device 5, as appropriate. This enables the secondSOC to be maintained within the medium-SOC area as much as possible.Therefore, the progression of deterioration of the second energy storagedevice 6 can be minimized. In addition, a portion of the capacity of thesecond energy storage device 6 which is used in the CS mode, describedbelow, can be saved as much as possible.

Furthermore, when the second energy storage device 6 is charged, thebase amount of power supplied P1_base output from the first energystorage device 5 is set in accordance with the second SOC regardless ofthe required output DM_dmd. Thus, the output P2 or the input Pc2 of thesecond energy storage device 6 changes in response to a change in therequired output DM_dmd, and the change in the output P1 of the firstenergy storage device 5 is less sensitive to the change in the requiredoutput DM_dmd.

In particular, the base amount of power supplied P1_base in the low-SOCarea is a constant value (=P1b). This prevents the output P1 of thefirst energy storage device 5 from changing in accordance with thechange in required driving force DT_dmd.

As a result, in the situation where the second energy storage device 6is charged (when the amount of power supplied corresponding to therequired output DM_dmd is less than the base amount of power suppliedP1_base), the output P1 of the first energy storage device 5 is of highstability with less frequent changes. Therefore, the progression ofdeterioration of the first energy storage device 5 can be minimized.

In this embodiment, when the second SOC is greater than or equal to thepredetermined value B2d, if the amount of power supplied correspondingto the required output DM_dmd is less than or equal to the thresholdDM_th1, power is supplied from only the first energy storage device 5 tothe electric motor 3. This can reduce the load on the second energystorage device 6 when the second SOC is greater than or equal to thepredetermined value B2d, resulting in the total amount of heatgeneration of the first energy storage device 5 and the second energystorage device 6 being reduced.

FIG. 8 is a graph illustrating how the respective amounts of heatgeneration of the energy storage devices 5 and 6 and the total amount ofheat generation of the energy storage devices 5 and 6 change in responseto a change in percentage shares X1 and X2 of the constant requiredoutput DM_dmd for the first energy storage device 5 and the secondenergy storage device 6.

The percentage share X1 refers to the proportion of a share of theamount of power supplied corresponding to the constant required outputDM_dmd that is taken on by the first energy storage device 5, and thepercentage share X2 refers to the proportion of a share of the amount ofpower supplied corresponding to the constant required output DM_dmd thatis taken on by the second energy storage device 6.

The second energy storage device 6 with relatively high power densityhas a lower impedance (internal resistance) than the first energystorage device 5 with relatively high energy density but includes fewercells connected in parallel than the first energy storage device 5, andtherefore has a lower output voltage than the first energy storagedevice 5. For this reason, when the percentage share X2 for the secondenergy storage device 6 is increased with respect to a certain constantvalue of the required output DM_dmd, the amount of heat generation ofthe second energy storage device 6 is more likely to increase than whenthe percentage share X1 for the first energy storage device 5 isincreased (see two thin lines in the graph illustrated in FIG. 8).

As a result, as indicated by a thick line in the graph illustrated inFIG. 8, the total amount of heat generation of the first energy storagedevice 5 and the second energy storage device 6 becomes minimum when thepercentage share X1 is greater than the percentage share X2.

In this embodiment, accordingly, when the second SOC is greater than orequal to the predetermined value B2d, if the amount of power suppliedcorresponding to the required output DM_dmd is less than or equal to thethreshold DM_th1, power is supplied from only the first energy storagedevice 5 to the electric motor 3 to reduce the load on the second energystorage device 6 to such an extent that the load placed on the firstenergy storage device 5 does not become excessive.

This configuration can minimize the total amount of heat generation ofthe first energy storage device 5 and the second energy storage device 6while preventing the second energy storage device 6 from generatingexcessive heat. In other words, the demand can be prevented from beingconcentrated in one of the first energy storage device 5 and the secondenergy storage device 6.

Control Process During Regenerative Operation in CD Mode

Next, a control process executed by the power transmission controller 32during the regenerative operation of the electric motor 3 in the CD modewill be described in detail hereinafter with reference to FIGS. 9 and10.

FIG. 9 is a map that defines how the regenerative power output by theelectric motor 3 during the regenerative operation in the CD mode isshared in order to charge the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required amount ofregeneration G_dmd of the electric motor 3 and the second SOC.

In FIG. 9, diagonally hatched areas represent areas where all or part ofthe regenerative power generated by the electric motor 3 is used tocharge the first energy storage device 5, and a shaded area representsan area where all or part of the regenerative power is used to chargethe second energy storage device 6.

More specifically, the lower diagonally hatched area in the medium-SOCarea and the high-SOC area of the second SOC represents an area whereall of the regenerative power is used to charge only the first energystorage device 5. The shaded area in the medium-SOC area and thehigh-SOC area of the second SOC and the upper diagonally hatched area inthe low-SOC area and the medium-SOC area represent areas where theregenerative power is used to charge both the first energy storagedevice 5 and the second energy storage device 6. The shaded area in thelow-SOC area of the second SOC represents an area where all of theregenerative power is used to charge only the second energy storagedevice 6.

On the map illustrated in FIG. 9, G_max1 is a maximum value of therequired amount of regeneration G_dmd in the CD mode. The maximum valueG_max1 is a constant value when the second SOC is an SOC less than orequal to a predetermined value B2f in the high-SOC area. When the secondSOC is larger than the value B2f, the maximum value G_max1 decreases asthe second SOC increases.

The control process for the power transmission controller 32 during theregenerative operation of the electric motor 3 in the CD mode issequentially executed in a predetermined control process cycle inaccordance with a flowchart illustrated in FIG. 10 by using the mapillustrated in FIG. 9.

In STEP51, the power transmission controller 32 acquires the requiredamount of regeneration G_dmd and a detected value of the second SOC.

Then, in STEP52, the power transmission controller 32 determines whetheror not the required amount of regeneration G_dmd is less than or equalto a predetermined threshold G_th1.

In this embodiment, the threshold G_th1 is set in accordance with thesecond SOC. Specifically, as illustrated in the example in FIG. 9, whenthe second SOC falls within the high-SOC area, the threshold G_th1 isset to a predetermined constant value.

When the second SOC falls within the medium-SOC area, the thresholdG_th1 is set to successively decrease from the constant value to zero inaccordance with the decrease in the second SOC. In the low-SOC area ofthe second SOC, the threshold G_th1 is set to zero.

The amount of charging power corresponding to a maximum value of thethreshold G_th1 (the constant value in the high-SOC area) is an upperlimit on the amount of regenerative power used to charge the firstenergy storage device 5. The upper limit is determined to be acomparatively small value so as to allow the first energy storage device5 to be charged at a low rate (low speed) to minimize the progression ofdeterioration of the first energy storage device 5.

For additional explanation, the amount of charging power correspondingto a certain threshold for the required amount of regeneration G_dmdrefers to the amount of electricity representing the total regenerativepower output from the electric motor 3 when the required amount ofregeneration G_dmd matches this threshold.

The determination result of STEP52 is affirmative for the lowerdiagonally hatched area illustrated in FIG. 9. In this situation, inSTEP53, the power transmission controller 32 controls the voltageconverter 23 and the inverter 21 of the power transmission circuit unit7 so that an input Pc1 of the first energy storage device 5 matches theamount of charging power corresponding to the required amount ofregeneration G_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block charging of thesecond energy storage device 6.

The input Pc1 of the first energy storage device 5 is specifically anamount of electricity used to charge the first energy storage device 5(the amount of charging power), and the input Pc2 of the second energystorage device 6 (described below) is specifically an amount ofelectricity used to charge the second energy storage device 6 (an amountof charging power). The amount of charging power corresponding to therequired amount of regeneration G_dmd refers to the amount ofelectricity representing the regenerative power output from the electricmotor 3 when the regenerative operation of the electric motor 3 isperformed in accordance with the required amount of regeneration G_dmd.

For additional explanation, when the detected value of the second SOCduring the regenerative operation of the electric motor 3 falls withinthe low-SOC area, the threshold G_th1 is zero and thus no affirmativedetermination is made in STEP52. Thus, in this case, the processing ofSTEP53 is not executed.

If the determination result of STEP52 is negative, then, in STEP54, thepower transmission controller 32 determines whether or not the requiredamount of regeneration G_dmd is less than or equal to a predeterminedthreshold G_th2.

In this embodiment, the threshold G_th2 is set in accordance with thesecond SOC in a way similar to that for the threshold G_th1 in STEP52described above. Specifically, as illustrated in the example in FIG. 9,when the second SOC falls within the low-SOC area, the threshold G_th2is set to a predetermined constant value. The constant value is set sothat the amount of charging power corresponding to the differencebetween the threshold G_th2 and the maximum value G_max1 of the requiredamount of regeneration G_dmd (=G_max1−G_th2) matches the amount ofcharging power corresponding to the maximum value of the threshold G_th1(the value of the threshold G_th1 in the high-SOC area), that is, theupper limit on the amount of charging power of the first energy storagedevice 5.

When the second SOC falls within the medium-SOC area, the thresholdG_th2 is set to increase to the maximum value G_max1 in accordance withthe increase in the second SOC in a pattern similar to the pattern inwhich the threshold G_th1 changes. In the high-SOC area of the secondSOC, the threshold G_th1 is kept at the constant maximum value G_max1.

In the medium-SOC area, the thresholds G_th1 and G_th2 are set so thatthe sum of the amount of charging power corresponding to the differencebetween the maximum value G_max1 and the threshold G_th2 (=G_max1−G_th2)and the amount of charging power corresponding to the threshold G_th1matches the upper limit on the amount of charging power of the firstenergy storage device 5.

The determination result of STEP54 is affirmative for the shaded areaillustrated in FIG. 9. In this situation, in STEP55, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc1 of the first energy storage device 5 matches the amount ofcharging power corresponding to the threshold G_th1 and so that theinput Pc2 of the second energy storage device 6 matches the amount ofcharging power obtained by subtracting the input Pc1 of the first energystorage device 5 from the amount of charging power corresponding to therequired amount of regeneration G_dmd.

On the other hand, the determination result of STEP54 is negative forthe upper diagonally hatched area in the low-SOC area or the medium-SOCarea illustrated in FIG. 9. In this situation, in STEP56, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc2 of the second energy storage device 6 matches the amount ofcharging power corresponding to the difference between the thresholdsG_th1 and G_th2 (=G_th2−G_th1) and so that the input Pc1 of the firstenergy storage device 5 matches the amount of charging power obtained bysubtracting the input Pc2 of the second energy storage device 6 from theamount of charging power corresponding to the required amount ofregeneration G_dmd.

For additional explanation, when the detected value of the second SOCduring the regenerative operation of the electric motor 3 falls withinthe high-SOC area, the threshold G_th2 matches the maximum value G_max1and thus no negative determination is made in STEP54. Thus, in thiscase, the processing of STEP56 is not executed.

The control process during the regenerative operation of the electricmotor 3 in the CD mode is executed in the way described above. In thiscontrol process, when the detected value of the second SOC is largerthan the threshold B2_th2, which is the lower limit of the medium-SOCarea, the first energy storage device 5 is preferentially charged withregenerative power in the range where the required amount ofregeneration G_dmd is less than or equal to the threshold G_th1.

Further, when the detected value of the second SOC is smaller than thethreshold B2_th1, which is the upper limit of the medium-SOC area, thefirst energy storage device 5 is charged with regenerative power withina range where the required amount of regeneration G_dmd is larger thanthe threshold G_th2.

The amount of regenerative power used to charge the first energy storagedevice 5 is limited to a value less than or equal to a predeterminedupper limit (the amount of charging power corresponding to the thresholdG_th1 in the high-SOC area).

This configuration enables the first energy storage device 5 to becharged with regenerative power at a low rate. This can restore the SOCof the first energy storage device 5 while suppressing the progressionof deterioration of the first energy storage device 5.

When the detected value of the second SOC is smaller than the thresholdB2_th2, which is the lower limit of the medium-SOC area, the secondenergy storage device 6 is preferentially charged with regenerativepower. When the detected value of the second SOC is larger than thethreshold B2_th2, which is the lower limit of the medium-SOC area, thesecond energy storage device 6 is charged with regenerative power withina range where the required amount of regeneration G_dmd is larger thanthe threshold G_th1.

This configuration enables the second energy storage device 6 to becharged with regenerative power so that the SOC of the second energystorage device 6 can be kept within the medium-SOC area as much aspossible. As a result, the progression of deterioration of the secondenergy storage device 6 can be minimized, and a portion of the capacityof the second energy storage device 6 which is used in the CS mode,described below, can be saved as much as possible. Control Process forFirst CS Mode

Next, the control process for the first CS mode in STEP6 will bedescribed in detail with reference to FIGS. 11 to 15.

The control device 8 determines a required driving force (requiredpropulsion force) or required braking force of the entire vehicle in away similar to that in the CD mode and also determines the respectivetarget operating states of the internal combustion engine 2, theelectric motor 3, the electric generator 4, the clutch 11, and the brakedevice.

In the first CS mode, the control device 8 determines the necessity ofoperation of the internal combustion engine 2 and the necessity of powergeneration operation of the electric generator 4, if necessary, inaccordance with the required driving force or required braking force ofthe entire vehicle, the detected value of the second SOC, or the like,and controls the operation of the internal combustion engine 2 and theelectric generator 4 in accordance with the determination result.

In this case, the start of the internal combustion engine 2 and thepower generation operation of the electric generator 4 are performed inthe way described above in connection with the processing of STEP7.

In the vehicle driving request state (in the state where the requireddriving force is not zero) during the operation of the internalcombustion engine 2, the control device 8 determines the respectiveshares of the required driving force of the entire vehicle that aretaken on by the electric motor 3 and the internal combustion engine 2 inaccordance with the required driving force of the entire vehicle, thedetected values of the first SOC and the second SOC, and so on.

In this case, the respective shares for the electric motor 3 and theinternal combustion engine 2 are determined so that, basically, exceptfor the case where the second SOC is comparatively high, all or a largeportion of the required driving force is taken on by the internalcombustion engine 2 and the electric motor 3 serves in an auxiliaryrole.

The control device 8 causes the internal combustion engine operationcontroller 31 to control the motive power (output torque) of theinternal combustion engine 2 in accordance with the share of therequired driving force for the internal combustion engine 2, and alsocauses the clutch controller 33 to control the operating state of theclutch 11. In a situation where the power generation operation of theelectric generator 4 is performed, motive power necessary for the powergeneration operation of the electric generator 4 is added to the motivepower of the internal combustion engine 2.

Further, the control device 8 determines the required output DM_dmd ofthe electric motor 3 so that the share of the required driving force forthe electric motor 3 is satisfied by the motive power generated throughthe power-running operation of the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to supplypower from either or both of the first energy storage device 5 and thesecond energy storage device 6 to the electric motor 3 in accordancewith a pre-created map illustrated in FIG. 11 on the basis of therequired output DM_dmd and the detected value of the SOC of the firstenergy storage device 5 (i.e., the first SOC).

In the first CS mode, even in a situation where the share of therequired driving force for the electric motor 3 is zero (a situationwhere the power-running operation of the electric motor 3 is notperformed), the control device 8 causes the power transmissioncontroller 32 to control the voltage converters 23 and 24 of the powertransmission circuit unit 7 so that, when the detected value of thefirst SOC is comparatively small, the first energy storage device 5 ischarged with power supplied from the second energy storage device 6.

In the vehicle driving request state when the internal combustion engine2 is not in operation, the control device 8 determines the requiredoutput DM_dmd of the electric motor 3 so that the required driving forceof the entire vehicle is satisfied by the motive power generated throughthe power-running operation of the electric motor 3.

Then, similarly to when the internal combustion engine 2 is inoperation, the control device 8 causes the power transmission controller32 to control the inverter 21 on the electric motor 3 side and thevoltage converters 23 and 24 of the power transmission circuit unit 7 inaccordance with the map illustrated in FIG. 11 on the basis of therequired output DM_dmd and the detected value of the first SOC.

In the vehicle braking request state (in the state where the requiredbraking force is not zero), the control device 8 determines therespective shares of the required braking force of the entire vehiclefor the electric motor 3 and the brake device. In this case, the controldevice 8 determines the respective shares for the electric motor 3 andthe brake device on the basis of the magnitude of the required brakingforce, the detected value of the first SOC, and so on so as to basicallymaximize the share of the required braking force for the electric motor3.

Then, the control device 8 causes the brake controller 34 to control thebrake device in accordance with the share of the required braking forcefor the brake device.

Further, the control device 8 determines the required amount ofregeneration G_dmd of the electric motor 3 so that the share of therequired braking force for the electric motor 3 is satisfied by theregenerative braking force generated through the regenerative operationof the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to chargeeither or both of the first energy storage device 5 and the secondenergy storage device 6 with the regenerative power output from theelectric motor 3 in accordance with a pre-created map illustrated inFIG. 14 on the basis of the required amount of regeneration G_dmd andthe detected value of the second SOC. In this embodiment, the primaryenergy storage device to be charged with the regenerative power in thefirst CS mode is the second energy storage device 6.

The power generation operation of the electric generator 4 is stoppedduring the regenerative operation of the electric motor 3 or duringpower supply from the second energy storage device 6 to the electricmotor 3. Note that charging of the second energy storage device 6 withthe regenerative power of the electric motor 3 and charging of thesecond energy storage device 6 with the generated power of the electricgenerator 4 may be performed in parallel.

Control Process During Power-Running Operation in First CS Mode

A control process executed by the power transmission controller 32during the power-running operation of the electric motor 3 in the firstCS mode will be described in detail hereinafter with reference to FIGS.11 to 13.

FIG. 11 illustrates a map depicting how the output demand for the amountof electricity to be supplied (the amount of power supplied) to theelectric motor 3 is shared by the first energy storage device 5 and thesecond energy storage device 6 in the first CS mode in accordance withthe required output DM_dmd of the electric motor 3 and the first SOC.

In FIG. 11, diagonally hatched areas represent areas where all or partof the amount of power supplied to the electric motor 3 is taken on bythe first energy storage device 5, and a shaded area represents an areawhere all or part of the amount of power supplied to the electric motor3 is taken on by the second energy storage device 6.

More specifically, the lower diagonally hatched area represents an areawhere all the amount of power supplied to the electric motor 3 is takenon only by the first energy storage device 5, and a shaded arearepresents an area where the amount of power supplied to the electricmotor 3 is taken on only by the second energy storage device 6 or theamount of power supplied to the electric motor 3 is taken on by both thefirst energy storage device 5 and the second energy storage device 6.The upper diagonally hatched area represents an area where the amount ofpower supplied to the electric motor 3 is taken on by both the firstenergy storage device 5 and the second energy storage device 6.

On the map illustrated in FIG. 11, DM_max2 is a maximum value of therequired output DM_dmd in the first CS mode. The maximum value DM_max2is a constant value.

In the control process during the power-running operation of theelectric motor 3 in the first CS mode, as illustrated in FIG. 11, theshares for the respective outputs of the first energy storage device 5and the second energy storage device 6 are identified for the caseswhere the value of the first SOC falls within a high-SOC area(high-remaining-capacity area) and a low-SOC area(low-remaining-capacity area) in the range between the CD→CS switchingthreshold B1_mc1 (see FIG. 2) and the CS→CD switching threshold B1_mc2(see FIG. 2) described above. The high-SOC area is an area whereSOC≥B1_th1 is satisfied, and the low-SOC area is an area whereSOC<B1_th1 is satisfied. B1_th1 is a predetermined threshold (fixedvalue) between the CD→CS switching threshold B1_mc1 and the CS→CDswitching threshold B1_mc2.

The control process for the power transmission controller 32 during thepower-running operation of the electric motor 3 in the first CS mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 11 in accordance with a flowchartillustrated in FIGS. 12 and 13.

In STEP61, the power transmission controller 32 acquires the requiredoutput DM_dmd and a detected value of the first SOC. Then, in STEP62,the power transmission controller 32 determines whether or not thedetected value of the first SOC acquired in STEP61 is greater than orequal to the threshold B1_th1.

The determination result of STEP62 is affirmative in the situation wherethe detected value of the first SOC falls within the high-SOC area. Inthis case, then, in STEP63, the power transmission controller 32determines whether or not the required output DM_dmd is less than orequal to a predetermined threshold DM_th5.

As illustrated in FIG. 11, the threshold DM_th5 is a predeterminedconstant value (fixed value) when the first SOC is a value greater thanor equal to a predetermined value B1c that is slightly larger than thethreshold B1_th1. The constant value is a value sufficiently smallerthan the allowable upper limit on the amount of power supplied to beoutput from the first energy storage device 5.

In the area less than the value B1c (the range of B1c to B1_th1), thethreshold DM_th5 is set to decrease to zero in accordance with thedecrease in the first SOC.

The determination result of STEP63 is affirmative for the lowerdiagonally hatched area in the high-SOC area illustrated in FIG. 11. Inthis case, in STEP64, the power transmission controller 32 controls thevoltage converter 23 and the inverter 21 of the power transmissioncircuit unit 7 so that the output P1 of the first energy storage device5 matches the amount of power supplied corresponding to the requiredoutput DM_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block discharge from thesecond energy storage device 6.

If the determination result of STEP63 is negative, then, in STEP65, thepower transmission controller 32 determines whether or not the requiredoutput DM_dmd is less than or equal to a predetermined threshold DM_th6.

In this embodiment, the threshold DM_th6 is a threshold used for boththe high-SOC area and the low-SOC area of the second SOC. The thresholdDM_th6 is set to a threshold that is larger than the threshold DM_th5 bya predetermined amount in the high-SOC area, and is set to a thresholdthat is larger than zero by the predetermined amount (i.e., thethreshold is equal to the predetermined amount) in the low-SOC area.

In this case, the threshold DM_th6 can be set so that, for example, theamount of power supplied corresponding to the predetermined amount isequal to the allowable upper limit on the amount of power supplied forthe second energy storage device 6 in the first CS mode or an amount ofpower supplied which is close to the allowable upper limit.

The required output DM_dmd, which is less than or equal to the thresholdDM_th6, is in a commonly used range of the electric motor 3 in the firstCS mode.

The determination result of STEP65 is affirmative for the shaded area inthe high-SOC area illustrated in FIG. 11. In this case, in STEP66, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 21 of the power transmission circuit unit 7 so thatthe output P1 of the first energy storage device 5 matches the amount ofpower supplied corresponding to the threshold DM_th5 and so that theoutput P2 of the second energy storage device 6 matches the amount ofpower supplied which is obtained by subtracting the output P1 of thefirst energy storage device 5 from the amount of power suppliedcorresponding to the required output DM_dmd.

On the other hand, the determination result of STEP65 is negative forthe upper diagonally hatched area in the high-SOC area illustrated inFIG. 11. In this situation, in STEP67, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the amount of power suppliedcorresponding to the difference between the thresholds DM_th5 and DM_th6(=DM_th6−DM_th5) and so that the output P1 of the first energy storagedevice 5 matches the amount of power supplied which is obtained bysubtracting the output P2 of the second energy storage device 6 from theamount of power supplied corresponding to the required output DM_dmd.

The determination result of STEP62 is negative in the situation wherethe detected value of the first SOC falls within the low-SOC area. Inthis case, in STEP68 illustrated in FIG. 13, the power transmissioncontroller 32 further determines a base amount of power suppliedP2_base, which is a base value of the output P2 of the second energystorage device 6, in accordance with the detected value of the firstSOC.

The base amount of power supplied P2_base is a lower limit on the amountof electricity that is output from the second energy storage device 6regardless of the required output DM_dmd of the electric motor 3 whenthe detected value of the first SOC falls within the low-SOC area. Thatis, in this embodiment, when the detected value of the first SOC fallswithin the low-SOC area during the power-running operation of theelectric motor 3, the power transmission circuit unit 7 is controlled sothat the base amount of power supplied P2_base or a larger amount ofpower supplied is output from the second energy storage device 6regardless of the required output DM_dmd.

In this embodiment, in the first CS mode, the power transmission circuitunit 7 is controlled so that also in a situation where the power-runningoperation of the electric motor 3 is not performed (in a situation wherethe required driving force of the entire vehicle is taken on only by theinternal combustion engine 2), the base amount of power supplied P2_baseis output from the second energy storage device 6 to charge the firstenergy storage device 5.

The base amount of power supplied P2_base is determined from thedetected value of the first SOC on the basis of a pre-created map or acalculation formula so that the base amount of power supplied P2_basechanges in accordance with the first SOC in a pattern indicated by abroken line illustrated in FIG. 11, for example. In this case, the baseamount of power supplied P2_base is determined to successively increasefrom zero to a maximum value P2b in accordance with the decrease in thefirst SOC when the first SOC is an SOC in a range between the thresholdB1_th1 and a predetermined value B1d that is slightly smaller than thethreshold B1_th1, and is determined to be kept constant at the maximumvalue P2b in an area where the first SOC is less than or equal to thepredetermined value Bid. The maximum value P2b is a value smaller thanthe amount of power supplied corresponding to the threshold DM_th6 forthe required output DM_dmd in the low-SOC area of the first SOC. Themaximum value P2b is set so that, even if a large portion of the maximumvalue P2b is used to charge the first energy storage device 5, the firstenergy storage device 5 can be charged at a low rate at which theprogression of deterioration of the first energy storage device 5 can besuppressed.

After determining the base amount of power supplied P2_base in the waydescribed above, then, in STEP69, the power transmission controller 32determines whether or not the amount of power supplied corresponding tothe required output DM_dmd is smaller than the base amount of powersupplied P2_base.

The determination result of STEP69 is affirmative for an area below thebroken line within the shaded area in the low-SOC area illustrated inFIG. 11. In this situation, in STEP70, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the base amount of power suppliedP2_base and so that the input Pc1 (the amount of charging power) of thefirst energy storage device 5 matches the amount of power supplied whichis obtained by subtracting the amount of power supplied corresponding tothe required output DM_dmd from the base amount of power suppliedP2_base.

If the determination result of STEP69 is negative, in STEP71, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to the threshold DM_th6.

The determination result of STEP71 is affirmative for an area obtainedby removing the area below the broken line from the shaded area in thelow-SOC area illustrated in FIG. 11 (specifically, an area obtained bycombining the area along the broken line and an area above the brokenline).

In this situation, in STEP72, the power transmission controller 32controls the voltage converter 24 and the inverter 21 of the powertransmission circuit unit 7 so that the output P2 of the second energystorage device 6 matches the amount of power supplied corresponding tothe required output DM_dmd. In this case, the voltage converter 23 onthe first energy storage device 5 side is controlled to block dischargefrom the first energy storage device 5.

On the other hand, the determination result of STEP71 is negative forthe upper diagonally hatched area in the low-SOC area illustrated inFIG. 11. In this situation, in STEP73, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the amount of power suppliedcorresponding to the threshold DM_th6 in the low-SOC area and so thatthe output P1 of the first energy storage device 5 matches the amount ofpower supplied which is obtained by subtracting the output P2 of thesecond energy storage device 6 from the amount of power suppliedcorresponding to the required output DM_dmd.

The control process during the power-running operation of the electricmotor 3 in the first CS mode is executed in the way described above. Inthis control process, when the detected value of the first SOC fallswithin the low-SOC area, the output P2 of the second energy storagedevice 6 is retained at the base amount of power supplied P2_base, whichis set in accordance with the detected value of the first SOC, if theamount of power supplied corresponding to the required output DM_dmd isless than or equal to the base amount of power supplied P2_base.

If the amount of power supplied corresponding to the required outputDM_dmd is larger than the base amount of power supplied P2_base, theamount of power supplied corresponding to the required output DM_dmd,which is a portion of the base amount of power supplied P2_base, issupplied from only the second energy storage device 6 to the electricmotor 3 and, also, the first energy storage device 5 is charged with theamount of power supplied which is obtained by subtracting the amount ofpower supplied corresponding to the required output DM_dmd from the baseamount of power supplied P2_base. This can gradually restore the firstSOC.

In this case, furthermore, high-accuracy adjustment of the rate ofcharging of the first energy storage device 5 is achievable by the powertransmission controller 32 controlling the voltage converters 23 and 24.Accordingly, the first energy storage device 5 is charged at a low rate,resulting in the progression of deterioration of the first energystorage device 5 being more effectively suppressed than when the firstenergy storage device 5 is charged with the generated power output bythe electric generator 4 by using the motive power of the internalcombustion engine 2.

When the detected value of the first SOC falls within the high-SOC area,power is supplied preferentially from the first energy storage device 5to the electric motor 3 if the required output DM_dmd is less than orequal to the threshold DM_th5.

This configuration can reduce the load on the second energy storagedevice 6 in the first CS mode, and prevent the second energy storagedevice 6 from generating excessive heat. Control Process duringRegenerative Operation in First CS Mode

Next, a control process executed by the power transmission controller 32during the regenerative operation of the electric motor 3 in the firstCS mode will be described in detail hereinafter with reference to FIGS.14 and 15.

FIG. 14 is a map that defines how the regenerative power output by theelectric motor 3 during the regenerative operation in the first CS modeis shared in order to charge the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required amount ofregeneration G_dmd of the electric motor 3 and the first SOC (the firstSOC in the range between the CD→CS switching threshold B1_mc1 and theCS→CD switching threshold B1_mc2).

In FIG. 14, a diagonally hatched area represents an area where all orpart of the regenerative power generated by the electric motor 3 is usedto charge the first energy storage device 5, and a shaded arearepresents an area where all or part of the regenerative power is usedto charge the second energy storage device 6.

On the map illustrated in FIG. 14, G_max2 is a maximum value of therequired amount of regeneration G_dmd in the first CS mode. The maximumvalue G_max2 is a constant value when the first SOC is an SOC less thanor equal to a predetermined value B1e that is slightly smaller than theCS→CD switching threshold B1_mc2. When the first SOC is larger than thevalue B1e, the maximum value G_max2 decreases in accordance with theincrease in the first SOC.

A control process for the power transmission controller 32 during theregenerative operation of the electric motor 3 in the first CS mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 14 in accordance with a flowchartillustrated in FIG. 15.

In STEP81, the power transmission controller 32 acquires the requiredamount of regeneration G_dmd and a detected value of the first SOC.

Then, in STEP82, the power transmission controller 32 determines whetheror not the required amount of regeneration G_dmd is less than or equalto a predetermined threshold (a charging threshold) G_th4.

In this embodiment, the threshold G_th4 is set in accordance with thefirst SOC. Specifically, as illustrated in the example in FIG. 14, thethreshold G_th4 is set to a predetermined constant value when the firstSOC is an SOC less than or equal to the predetermined value B1e. Theconstant value is determined to be a comparatively small value so as toallow the first energy storage device 5 to be charged at a low rate (lowspeed) to minimize the progression of deterioration of the first energystorage device 5.

When the first SOC is larger than the predetermined value B1e, thethreshold G_th4 is set to successively decrease from the constant valueto zero (reach zero at the CS→CD switching threshold B1_mc2) inaccordance with the decrease in the first SOC.

The determination result of STEP82 is affirmative for the diagonallyhatched area illustrated in FIG. 14. In this situation, in STEP83, thepower transmission controller 32 controls the voltage converter 23 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc1 of the first energy storage device 5 matches the amount ofcharging power corresponding to the required amount of regenerationG_dmd. In this case, the voltage converter 24 on the second energystorage device 6 side is controlled to block charging of the secondenergy storage device 6.

On the other hand, the determination result of STEP82 is negative forthe shaded area illustrated in FIG. 14. In this situation, in STEP84,the power transmission controller 32 controls the voltage converters 23and 24 and the inverter 21 of the power transmission circuit unit 7 sothat the input Pc1 of the first energy storage device 5 matches theamount of charging power corresponding to the threshold G_th4 and sothat the input Pc2 of the second energy storage device 6 matches theamount of charging power obtained by subtracting the input Pc1 of thefirst energy storage device 5 from the amount of charging powercorresponding to the required amount of regeneration G_dmd.

The control process during the regenerative operation of the electricmotor 3 in the first CS mode is executed in the way described above.This control process allows the first energy storage device 5 to bepreferentially charged with regenerative power if the required amount ofregeneration G_dmd is less than or equal to the threshold G_th4. Inaddition, the amount of charging power of the first energy storagedevice 5 is limited to a value less than or equal to the amount ofcharging power corresponding to the threshold G_th4. This can restorethe first SOC while minimizing the progression of deterioration of thefirst energy storage device 5.

Control Process for Second CS Mode

Next, the control process for the second CS mode in STEP8 will bedescribed in detail with reference to FIGS. 16 to 20.

The control device 8 determines a required driving force (requiredpropulsion force) or required braking force of the entire vehicle in away similar to that in the CD mode, and also determines the respectivetarget operating states of the internal combustion engine 2, theelectric motor 3, the electric generator 4, the clutch 11, and the brakedevice.

In the second CS mode, the control device 8 causes the internalcombustion engine operation controller 31 to control the internalcombustion engine 2 to successively perform the operation of theinternal combustion engine 2. In addition to this, the control device 8causes the power transmission controller 32 to control the electricgenerator 4 to continuously perform the power generation operation ofthe electric generator 4, except during the rotation operation of theelectric motor 3. In this case, the power transmission controller 32controls the voltage converter 24 and the inverter 22 of the powertransmission circuit unit 7 so that only the second energy storagedevice 6, out of the first energy storage device 5 and the second energystorage device 6, is charged with the generated power corresponding tothe target value.

In the vehicle driving request state (in the state where the requireddriving force is not zero), the control device 8 determines therespective shares of the required driving force of the entire vehiclethat are taken on by the electric motor 3 and the internal combustionengine 2 in accordance with the required driving force of the entirevehicle, the detected value of the first SOC, and so on.

In this case, the respective shares for the electric motor 3 and theinternal combustion engine 2 are determined so that, basically, all or alarge portion of the required driving force is taken on by the internalcombustion engine 2 and the electric motor 3 serves in an auxiliaryrole.

The control device 8 causes the internal combustion engine operationcontroller 31 to perform control so that the motive power (outputtorque) of the internal combustion engine 2 is equal to motive powerincluding the motive power corresponding to the share of the requireddriving force for the internal combustion engine 2 and the motive powernecessary for the power generation operation of the electric generator4, and also causes the clutch controller 33 to control the clutch 11 toenter the connected state.

Further, the control device 8 determines the required output DM_dmd ofthe electric motor 3 so that the share of the required driving force forthe electric motor 3 is satisfied by the motive power generated throughthe power-running operation of the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverter 23 of the power transmission circuit unit 7 to supply powerfrom only the first energy storage device 5 to the electric motor 3 inaccordance with a pre-created map illustrated in FIG. 16 on the basis ofthe required output DM_dmd and the detected value of the SOC of thefirst energy storage device 5 (i.e., the first SOC).

In the vehicle braking request state (in the state where the requiredbraking force is not zero), the control device 8 determines therespective shares of the required braking force of the entire vehiclefor the electric motor 3 and the brake device. In this case, the controldevice 8 determines the respective shares for the electric motor 3 andthe brake device on the basis of the magnitude of the required brakingforce, the detected value of the first SOC, and so on so as to basicallymaximize the share of the required braking force for the electric motor3.

Then, the control device 8 causes the brake controller 34 to control thebrake device in accordance with the share of the required braking forcefor the brake device.

Further, the control device 8 determines the required amount ofregeneration G_dmd of the electric motor 3 so that the share of therequired braking force for the electric motor 3 is satisfied by theregenerative braking force generated through the regenerative operationof the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to chargeeither or both of the first energy storage device 5 and the secondenergy storage device 6 with the regenerative power output from theelectric motor 3 in accordance with a pre-created map illustrated inFIG. 18 on the basis of the required amount of regeneration G_dmd andthe detected value of the first SOC. In this embodiment, the primaryenergy storage device to be charged with the regenerative power in thesecond CS mode is the second energy storage device 6.

Control Process During Power-Running Operation in Second CS Mode

A control process executed by the power transmission controller 32during the power-running operation of the electric motor 3 in the secondCS mode will be described in detail hereinafter with reference to FIGS.16 and 17.

FIG. 16 illustrates a map depicting how the output demand for the amountof electricity to be supplied (the amount of power supplied) to theelectric motor 3 is shared by the first energy storage device 5 and thesecond energy storage device 6 in the second CS mode in accordance withthe required output DM_dmd of the electric motor 3 and the first SOC.

In FIG. 16, a diagonally hatched area represents an area where all theamount of power supplied to the electric motor 3 is taken on by thefirst energy storage device 5. On the map illustrated in FIG. 16,DM_max3 is a maximum value of the required output DM_dmd in the secondCS mode. The maximum value DM_max1 is a constant value.

In the control process during the power-running operation of theelectric motor 3 in the second CS mode, as illustrated in FIG. 16, theamount of power supplied to the electric motor 3 is always taken on onlyby the first energy storage device 5 within the entire range between theCD→CS switching threshold B1_mc1 (see FIG. 2) and the CS→CD switchingthreshold B1_mc2 (see FIG. 2) for the first SOC. In the second CS mode,accordingly, power supply from the second energy storage device 6 to theelectric motor 3 is disabled.

The control process for the power transmission controller 32 during thepower-running operation of the electric motor 3 in the second CS mode issequentially executed in a predetermined control process cycle inaccordance with a flowchart illustrated in FIG. 17.

In STEP91, the power transmission controller 32 acquires the requiredoutput DM_dmd. Then, in STEP92, the power transmission controller 32controls the voltage converter 23 and the inverter 21 of the powertransmission circuit unit 7 so that the output P1 of the first energystorage device 5 matches the amount of power supplied corresponding tothe required output DM_dmd.

The control process during the power-running operation of the electricmotor 3 in the second CS mode is executed in the way described above. Inthis control process, power supply from the second energy storage device6 to the electric motor 3 is disabled. This can quickly restore the SOCof the second energy storage device 6 with the generated power of theelectric generator 4.

Control Process During Regenerative Operation in Second CS Mode

Next, a control process executed by the power transmission controller 32during the regenerative operation of the electric motor 3 in the secondCS mode will be described in detail hereinafter with reference to FIGS.18 and 19.

FIG. 18 is a map that defines how the regenerative power output by theelectric motor 3 during the regenerative operation in the second CS modeis shared in order to charge the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required amount ofregeneration G_dmd of the electric motor 3 and the first SOC (the firstSOC in the range between the CD→CS switching threshold B1_mc1 and theCS→CD switching threshold B1_mc2).

In FIG. 18, diagonally hatched areas represent areas where all or partof the regenerative power generated by the electric motor 3 is used tocharge the first energy storage device 5, and a shaded area representsan area where all or part of the regenerative power is used to chargethe second energy storage device 6.

On the map illustrated in FIG. 18, G_max3 is a maximum value of therequired amount of regeneration G_dmd in the second CS mode. The maximumvalue G_max1 is a constant value.

A control process for the power transmission controller 32 during theregenerative operation of the electric motor 3 in the second CS mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 18 in accordance with a flowchartillustrated in FIG. 19.

In STEP101, the power transmission controller 32 acquires the requiredamount of regeneration G_dmd and a detected value of the first SOC.

Then, in STEP102, the power transmission controller 32 determineswhether or not the required amount of regeneration G_dmd is less than orequal to a predetermined threshold (a charging threshold) G_th5.

In this embodiment, the threshold G_th5 is set in accordance with thefirst SOC. Specifically, as illustrated in the example in FIG. 18, thethreshold G_th5 is set to a predetermined constant value when the firstSOC is an SOC less than or equal to a predetermined value B1f that isslightly smaller than the threshold B1 th1. The constant value isdetermined to be a comparatively small value so as to allow the firstenergy storage device 5 to be charged at a low rate (low speed) tominimize the progression of deterioration of the first energy storagedevice 5.

When the first SOC is larger than the predetermined value B1f, thethreshold G_th5 is set to successively decrease from the constant valueto zero (reach zero at the threshold B1_th1) in accordance with theincrease in the first SOC. When the first SOC is an SOC greater than orequal to the threshold B1_th1, the threshold G_th5 is kept at zero.

The determination result of STEP102 is affirmative for the lowerdiagonally hatched area illustrated in FIG. 18. In this situation, inSTEP103, the power transmission controller 32 controls the voltageconverter 23 and the inverter 21 of the power transmission circuit unit7 so that the input Pc1 of the first energy storage device 5 matches theamount of charging power corresponding to the required amount ofregeneration G_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block charging of thesecond energy storage device 6.

For additional explanation, when the detected value of the first SOC isgreater than or equal to the threshold B1_th1, the threshold G_th5 iszero and thus no affirmative determination is made in STEP102. Thus, inthis case, the processing of STEP103 is not executed.

If the determination result of STEP102 is negative, then, in STEP104,the power transmission controller 32 determines whether or not therequired amount of regeneration G_dmd is less than or equal to apredetermined threshold G_th6.

In this embodiment, the threshold G_th6 is set in accordance with thefirst SOC in a way similar to that for the threshold G_th5 in STEP102described above. Specifically, as illustrated in the example in FIG. 18,when the first SOC is an SOC greater than or equal to the thresholdB1_th1, the threshold G_th6 is set to a predetermined constant value.The constant value is set so that the amount of charging powercorresponding to the difference between the threshold G_th6 and themaximum value G_max1 of the required amount of regeneration G_dmd(=G_max3−G_th6) matches the amount of charging power corresponding tothe maximum value of the threshold G_th5 (the value of the thresholdG_th5 when the first SOC is less than or equal to the threshold B1f)(the amount of charging power by which the first energy storage device 5can be charged at a low rate).

When the first SOC is smaller than the threshold B1 th1, the thresholdG_th6 is set to increase to the maximum value G_max3 (reach the maximumvalue G_max3 at the threshold B1f) in accordance with the decrease inthe first SOC in a pattern similar to the pattern in which the thresholdG_th5 changes. When the first SOC is less than or equal to the thresholdB1f, the threshold G_th6 is maintained at the maximum value G_max3.

The thresholds G_th5 and G_th6 are set so that, within the range of B1fto B1_th1 of the first SOC, the thresholds G_th5 and G_th6 are set sothat the sum of the amount of charging power corresponding to thedifference between the maximum value G_max3 and the threshold G_th6(=G_max3−G_th6) and the amount of charging power corresponding to thethreshold G_th5 matches the amount of charging power corresponding tothe maximum value of the threshold G_th5 (the amount of charging powerby which the first energy storage device 5 can be charged at a lowrate).

The determination result of STEP104 is affirmative for the shaded areaillustrated in FIG. 18. In this situation, in STEP105, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc1 of the first energy storage device 5 matches the amount ofcharging power corresponding to the threshold G_th5 and so that theinput Pc2 of the second energy storage device 6 matches the amount ofcharging power obtained by subtracting the input Pc1 of the first energystorage device 5 from the amount of charging power corresponding to therequired amount of regeneration G_dmd.

On the other hand, the determination result of STEP104 is negative forthe upper diagonally hatched area illustrated in FIG. 18. In thissituation, in STEP106, the power transmission controller 32 controls thevoltage converters 23 and 24 and the inverter 21 of the powertransmission circuit unit 7 so that the input Pc2 of the second energystorage device 6 matches the amount of charging power corresponding tothe difference between the thresholds G_th5 and G_th6 (=G_th6−G_th5) andso that the input Pc1 of the first energy storage device 5 matches theamount of charging power obtained by subtracting the input Pc2 of thesecond energy storage device 6 from the amount of charging powercorresponding to the required amount of regeneration G_dmd.

For additional explanation, when the first SOC is less than or equal tothe predetermined value B1f, the threshold G_th6 matches the maximumvalue G_max3 and thus no negative determination is made in STEP104.Thus, in this case, the processing of STEP106 is not executed.

The control process during the regenerative operation of the electricmotor 3 in the second CS mode is executed in the way described above. Inthis control process, when the detected value of the first SOC is largerthan the threshold B1_th1, all or a large portion of the regenerativepower is used to charge the second energy storage device 6. Thus, theSOC of the second energy storage device 6 may be effectively restoredwith regenerative power.

In the second CS mode, the second energy storage device 6 is chargedwith generated power produced by the electric generator 4, except duringthe regenerative operation of the electric motor 3. Both the generatedpower and the regenerative power can be used to quickly restore the SOCof the second energy storage device 6 toward the CS2→CS1 switchingthreshold B2_mc2.

When the detected value of the first SOC is smaller than the thresholdB1_th1, the first energy storage device 5 is preferentially charged withregenerative power within the range where the required amount ofregeneration G_dmd is less than or equal to the threshold G_th5.Further, when the detected value of the first SOC is larger than thepredetermined value B1f, the first energy storage device 5 is chargedwith regenerative power within the range where the required amount ofregeneration G_dmd is larger than the threshold G_th6. The amount ofcharging power of the first energy storage device 5 is limited to avalue less than or equal to the amount of charging power correspondingto the maximum value of the threshold G_th5. This can suppress areduction in the first SOC in the second CS mode while minimizing theprogression of deterioration of the first energy storage device 5.

A detailed description has been made of the control process for thecontrol device 8 in this embodiment.

The correspondences between this embodiment and the embodimentsdisclosed herein will now be briefly explained below. In thisembodiment, the first CS mode and the second CS mode correspond to afirst mode and a second mode in the embodiments disclosed herein,respectively.

The electric motor 3 corresponds to an electrical load or actuator inthe embodiments disclosed herein. The threshold B1_th1 for the first SOCcorresponds to a predetermined threshold for a first charge rate in theembodiments disclosed herein.

Further, on the map of the shares for power supply in the first CS mode(FIG. 11), the threshold DM_th6 in the low-SOC area of the first SOCcorresponds to an A-th threshold (a first maximum supplying amount) inthe embodiments disclosed herein, and the thresholds DM_th5 and DM_th6in the high-SOC area correspond to a B-th threshold (a second maximumsupplying amount) and a C-th threshold (a sum of the second maximumsupplying amount and a third maximum supplying amount) in theembodiments disclosed herein, respectively.

Further, the range of B1_mc1 to B1_mc2 on the map of the shares forcharging in the first CS mode (FIG. 14) and the range of B1_mc1 toB1_th1 on the map of the shares for charging in the second CS mode (FIG.18) correspond to a predetermined range for the first charge rate in theembodiments disclosed herein. In this case, the predetermined range ofB1_mc1 to B1_mc2 in the first CS mode (first mode) is extended withrespect to the predetermined range of B1_mc1 to B1_th1 in the second CSmode (second mode) toward the side on which the first SOC increases.

In this embodiment, the range of the first SOC (the range of B1a (%) toB1b (%) illustrated in FIG. 2) used for supplying power to the electricmotor 3 in the CD mode is larger than the range of the second SOC (therange of B2a (%) to B2b (%) illustrated in FIG. 2) used for supplyingpower to the electric motor 3 in the CD mode. Further, the range of thesecond SOC (the range of B2b (%) to B2c (%) illustrated in FIG. 2) usedfor supplying power to the electric motor 3 in the CS mode is largerthan the range of the first SOC (part of the range less than or equal toB1b (%) illustrated in FIG. 2) used for supplying power to the electricmotor 3 in the CS mode.

Furthermore, power to be supplied to the electric generator 4, whichserves as a starter actuator, when the internal combustion engine 2 isstarted in the CS mode is reserved in only the second energy storagedevice 6.

For this reason, a large portion of the power (stored energy) in thefirst energy storage device 5 with relatively high energy density can beutilized as power to be supplied to the electric motor 3 in the CD mode.As a result, the period during which power can be supplied from thefirst energy storage device 5 to the electric motor 3 in the CD mode,and therefore the drivable range of the vehicle in the CD mode in whichfuel consumption of the internal combustion engine 2 does not occur oris suppressed, can be maximized. In addition, the environmentalperformance of the motive power system 1 is improved.

In addition, part of the power in the second energy storage device 6(the stored energy within the range of B2a (%) to B2b (%) illustrated inFIG. 2) is usable as dedicated power to be supplied to the electricmotor 3 in the CD mode. This allows power to be supplied from the secondenergy storage device 6 with relatively high power density to theelectric motor 3 in an auxiliary manner, as necessary. Thus, the runningperformance of the vehicle (the driving performance of the drive wheelDW) in the CD mode can be enhanced.

In the first CS mode within the CS mode, the second energy storagedevice 6 can be used as the primary power supply for the electric motor3. Thus, the motive power of the electric motor 3 can be transmitted tothe drive wheel DW in an auxiliary manner with high responsivity to achange in the required driving force of the vehicle. As a result, therunning performance of the vehicle (the driving performance of the drivewheel DW) in the first CS mode can be enhanced.

In addition, part of the power in the first energy storage device 5(part of the range less than or equal to B1b (%) illustrated in FIG. 2)is usable as power to be supplied to the electric motor 3 in the CSmode. This allows power to be supplied, in particular, in the second CSmode, from the first energy storage device 5, instead of the secondenergy storage device 6, to the electric motor 3, as necessary. This caneliminate power supply from the second energy storage device 6 to theelectric motor 3 in the second CS mode. Thus, restoration of the SOC ofthe second energy storage device 6 in the second CS mode can beaccelerated.

In this embodiment, furthermore, in the second CS mode, the generatedpower of the electric generator 4 is used to charge only the secondenergy storage device 6. Part of the power used to charge the secondenergy storage device 6 in this manner is transferred from the secondenergy storage device 6 to the first energy storage device 5 in thefirst CS mode. In this case, in the first CS mode, the first energystorage device 5 can be charged stably at a low rate. This can minimizethe progression of deterioration of the first energy storage device 5.

FIG. 20 is a graph exemplifying schematic changes in the respective SOCsof the first energy storage device 5 and the second energy storagedevice 6 over time during the travel of the vehicle.

The period up to time t1 is the period of the CD mode. During thisperiod, the first SOC decreases basically. The second SOC changes inresponse to appropriate discharging and charging of the second energystorage device 6.

When the first SOC decreases to the CD→CS switching threshold B1_mc1 attime t1, the mode of the control process for the control device 8 isswitched to the first CS mode. The period from time t1 to time t2 is theperiod of the first CS mode. During the period of the first CS mode, thesecond SOC basically decreases in response to power supply to either orboth of the first energy storage device 5 and the electric motor 3. Thefirst SOC is gradually restored in response to appropriate charging ofthe first energy storage device 5 with power supplied from the secondenergy storage device 6.

When the second SOC decreases to the CS1→CS2 switching threshold B2_mc1at time t2, the mode of the control process for the control device 8 isswitched to the second CS mode. The period from time t2 to time t3 isthe period of the second CS mode. During the period of the second CSmode, the second SOC increases in response to charging of the secondenergy storage device 6 with generated power and regenerative power.

In the second CS mode, the first SOC decreases in a situation wherepower is supplied from the first energy storage device 5 to the electricmotor 3. In the second CS mode, however, since the second SOC is quicklyrestored by the generated power and the regenerative power, power supplyfrom the first energy storage device 5 to the electric motor 3 is notfrequently required in most cases. Thus, the reduction in the first SOCin the second CS mode does not so often occur.

When the second SOC is restored to the CS2→CS1 switching thresholdB2_mc2 at time t3, the mode of the control process for the controldevice 8 is switched to the first CS mode again. The period from time t3to time t4 is the period of the first CS mode. During the period of thefirst CS mode, as in the period from time t1 to time t2, the second SOCdecreases in response to power supply to either or both of the firstenergy storage device 5 and the electric motor 3, and the first SOC isgradually restored.

In the illustrated example, at time t4, the first SOC is restored to theCS→CD switching threshold B1_mc2. In response to the restoration, themode of the control process for the control device 8 is returned to theCD mode.

As described above, in the CS mode subsequent to the CD mode, the firstSOC can be gradually restored basically by alternately repeating thefirst CS mode and the second CS mode. As a result, the travel of thevehicle can be restarted in the CD mode in which only the motive powerof the electric motor 3 is used to drive the drive wheel DW.

MODIFICATIONS

There will now be described some modifications related to the embodimentdescribed above.

In the embodiment described above, the supply of power for causing theelectric generator 4 to operate as a starter actuator is taken on onlyby the second energy storage device 6. Alternatively, part of the powerto be supplied to the electric generator 4 may also be taken on by thefirst energy storage device 5. In this case, it is desirable that theload on the first energy storage device 5 be less than the load on thesecond energy storage device 6.

For utmost utilization of the power in the first energy storage device 5in the CD mode, it is desirable that all the power to be supplied to theelectric generator 4 be taken on by the second energy storage device 6.

In the embodiment described above, furthermore, power is supplied fromonly the first energy storage device 5 to the electric motor 3(discharge from the second energy storage device 6 is disabled) duringthe power-running operation of the electric motor 3 in the second CSmode. However, for example, if the required output DM_dmd is large, theamount of power supplied corresponding to part of the required outputDM_dmd may be supplied from the second energy storage device 6 to theelectric motor 3.

In the description of the embodiment described above, a transportationapparatus including the motive power system 1 is a hybrid vehicle, byway of example. The transportation apparatus is not limited to a vehicleand may be a ship, a railway carriage, or any other apparatus. Thedriven load may not necessarily be the drive wheel DW of a vehicle. Theactuator may be an actuator other than an electric motor.

A power supply system according to an aspect of the embodimentsdisclosed herein includes a first energy storage device, a second energystorage device having a higher power density and a lower energy densitythan the first energy storage device, a power transmission circuit unithaving a function of performing power transmission among an electricalload, the first energy storage device, and the second energy storagedevice, the electrical load being operated in response to power suppliedfrom at least one of the first energy storage device and the secondenergy storage device, and a control device that controls the powertransmission circuit unit to supply power from at least one of the firstenergy storage device and the second energy storage device to theelectrical load by performing a control process for a mode selected froma first mode and a second mode in accordance with a second charge ratethat is a charge rate of the second energy storage device, the firstmode and the second mode having different ways in which the powertransmission circuit unit is controlled, wherein the control device isconfigured to select the second mode when the second charge ratedecreases to a predetermined first switching threshold while the firstmode is selected, and to select the first mode when the second chargerate increases to a predetermined second switching threshold higher thanthe first switching threshold while the second mode is selected, acontrol process for the second mode is configured to control the powertransmission circuit unit in such a manner as to suppress discharge fromthe second energy storage device more than in a control process for thefirst mode, and the control process for at least the first mode, out ofthe first mode and the second mode, is configured to control the powertransmission circuit unit so that power shares to be supplied by thefirst energy storage device and the second energy storage device to theelectrical load are changed in accordance with a first charge rate thatis a charge rate of the first energy storage device (a first aspect ofthe embodiments).

In the embodiments, the “power transmission circuit unit” having afunction of performing power transmission among the first energy storagedevice, the second energy storage device, and the actuator refers to the“power transmission circuit unit” having at least a function capable ofcontrolling the amount of power supplied from each of the first energystorage device and the second energy storage device to the electricalload or having, in addition to this function, a function capable ofcontrolling selective switching of the source and destination of poweramong the first energy storage device, the second energy storage device,and the actuator.

Further, the term “amount of power supplied” described below refers tothe amount of electricity supplied from the first energy storage deviceor the second energy storage device to the target to which power issupplied. The target to which power is supplied is not limited to theactuator and may be an energy storage device (the first energy storagedevice or the second energy storage device). The “amount of electricity”or the “amount of power supplied” is expressed as an amount ofelectrical energy per unit time (e.g., a value of power) or an amount ofcharge per unit time (e.g., a value of current), for example.

A “required output” of the electrical load, described below, refers towhat defines a request value of the amount of electricity required forthe electrical load to operate. The request value of the amount ofelectricity itself may be used as the “required output”. If theelectrical load is designed to generate, for example, mechanical output(motive power or kinetic energy) corresponding to the amount ofelectricity to be supplied, a request value of the mechanical output canalso be used as the “required output” of the electrical load.

Further, the amount of power supplied corresponding to the “requiredoutput” refers to the amount of power to be supplied to the electricalload to realize the “required output”. Furthermore, the amount of powersupplied corresponding to a certain threshold (such as an A-th thresholddescribed below) for the required output refers to the amount of powersupplied corresponding to a required output when the required outputmatches the threshold.

According to the first aspect of the embodiments, switching from thefirst mode to the second mode is performed when the second charge ratedecreases to a predetermined first switching threshold, and switchingfrom the second mode to the first mode is performed when the secondcharge rate increases to a predetermined second switching thresholdhigher than the first switching threshold. This can avoid frequentswitching between the first mode and the second mode.

In the control process for the second mode, power supply from the secondenergy storage device to the electrical load is suppressed more than inthe control process for the first mode. This facilitates the restorationof the charge rate of the second energy storage device in the secondmode.

Examples of the process for restoring the charge rate of the secondenergy storage device in the second mode may include a process forcharging the second energy storage device with regenerative powergenerated by the electrical load through a regenerative operation and aprocess for charging the second energy storage device with powersupplied by the first energy storage device. If an electric generator isfurther included, a process for charging the second energy storagedevice with generated power of the electric generator is also available.

In the control process for at least the first mode, the powertransmission circuit unit is controlled so that power shares to besupplied by the first energy storage device and the second energystorage device when power is supplied to the electrical load are changedin accordance with the first charge rate.

In the control process for the first mode, therefore, it is possible tosupply power from either or both of the first energy storage device andthe second energy storage device to the electrical load in accordancewith the power shares suitable for the first charge rate.

According to the first aspect of the embodiments, therefore, it ispossible to supply power from two energy storage devices havingdifferent characteristics to an electrical load in an appropriatemanner.

In the first aspect of the embodiments, the control process for thefirst mode and the control process for the second mode may be configuredto control the power transmission circuit unit to supply power from atleast one of the first energy storage device and the second energystorage device to the electrical load in accordance with at least arequired output of the electrical load, and the control process for thesecond mode may be configured to control the power transmission circuitunit so that a range of the required output within which the secondenergy storage device is allowed to supply power to the electrical loadis smaller than a range of the required output within which the secondenergy storage device is allowed to supply power to the electrical loadin the control process for the first mode (a second aspect of theembodiments).

According to this configuration, it is possible to suppress power supplyfrom the second energy storage device to the electrical load moreappropriately in the control process for the second mode than in thecontrol process for the first mode.

In the first or second aspect of the embodiments, the control processfor the second mode may be configured to control the power transmissioncircuit unit to disable discharge from the second energy storage deviceand to permit power supply from the first energy storage device to theelectrical load (a third aspect of the embodiments).

According to this configuration, in the control process for the secondmode, discharge from the second energy storage device is disabled. Thisallows the charge rate of the second energy storage device to be morelikely to be restored in the second mode. In addition, a furtherreduction in the charge rate of the second energy storage device isavoidable, preventing the progression of deterioration of the secondenergy storage device.

In the first to third aspects of the embodiments, preferably, thecontrol process for the first mode is configured to include a processfor controlling the power transmission circuit unit to, when the firstcharge rate is lower than a predetermined threshold, supply, whileoutputting from the second energy storage device a predetermined baseamount of power supplied that is set regardless of a required output ofthe electrical load, an amount of power supplied corresponding to therequired output, which is part of the base amount of power supplied, tothe electrical load and charge the first energy storage device with anamount of power supplied which is equal to a difference obtained bysubtracting the amount of power supplied corresponding to the requiredoutput from the base amount of power supplied (a fourth aspect of theembodiments).

According to this configuration, in the first mode, when the firstcharge rate is lower than a predetermined threshold, the first energystorage device can be charged with power supplied from the second energystorage device. In this case, the first energy storage device is chargedby power transfer from the second energy storage device. This may makeit easy to control the power transmission circuit unit to perform thischarging operation at a low rate (low speed). In the first mode,therefore, it is possible to restore the charge rate of the first energystorage device while suppressing the progression of deterioration of thefirst energy storage device having high energy density.

In the fourth aspect of the embodiments, preferably, the control processfor the first mode is configured to control the power transmissioncircuit unit to, when the first charge rate is lower than thepredetermined threshold, if an amount of power supplied corresponding tothe required output is greater than the base amount of power suppliedand if the required output is less than or equal to a predetermined A-ththreshold, supply the amount of power supplied corresponding to therequired output from only the second energy storage device to theelectrical load (a fifth aspect of the embodiments).

This configuration can reduce the load on the first energy storagedevice when the first charge rate is lower than the predeterminedthreshold.

In the fifth aspect of the embodiments, preferably, the control processfor the first mode is configured to control the power transmissioncircuit unit to, when the first charge rate is lower than thepredetermined threshold, if the required output is greater than the A-ththreshold, supply an amount of power supplied corresponding to the A-ththreshold from the second energy storage device to the electrical loadand supply an amount of power supplied corresponding to a differencebetween the required output and the A-th threshold from the first energystorage device to the electrical load (a sixth aspect of theembodiments).

According to this configuration, in the first mode, when the firstcharge rate is lower than the predetermined threshold, the amount ofpower supplied from the second energy storage device to the electricalload can be limited to a value less than or equal to the amount of powersupplied corresponding to the A-th threshold. This can prevent the loadplaced on the second energy storage device from becoming excessive.

In the first to sixth aspects of the embodiments, preferably, thecontrol process for the first mode is configured to control the powertransmission circuit unit to, when the first charge rate is higher thana predetermined threshold, if a required output of the electrical loadis less than or equal to a predetermined B-th threshold, supply anamount of power supplied corresponding to the required output from onlythe first energy storage device to the electrical load (a seventh aspectof the embodiments).

According to this configuration, in the first mode, when the firstcharge rate is higher than the predetermined threshold, if the requiredoutput of the electrical load is low (less than or equal to apredetermined B-th threshold), power is supplied from only the firstenergy storage device to the electrical load. This can reduce the loadon the second energy storage device. It is therefore possible to preventrapid reduction in the charge rate of the second energy storage device.

In the seventh aspect of the embodiments, preferably, the controlprocess for the first mode is configured to control the powertransmission circuit unit to, when the first charge rate is higher thanthe predetermined threshold, if the required output is greater than theB-th threshold and is less than a predetermined C-th threshold, supplyan amount of power supplied corresponding to the B-th threshold from thefirst energy storage device to the electrical load and supply an amountof power supplied corresponding to a difference between the requiredoutput and the B-th threshold from the second energy storage device tothe electrical load (an eighth aspect of the embodiments).

According to this configuration, in the first mode, when the secondcharge rate is higher than the predetermined threshold, if the requiredoutput is greater than the B-th threshold and is less than apredetermined C-th threshold, the amount of power supplied from thefirst energy storage device to the electrical load is limited to theamount of power supplied corresponding to the B-th threshold. This canprevent the load placed on the first energy storage device from becomingexcessive. It is therefore possible to minimize the progression ofdeterioration of the first energy storage device.

In the eighth aspect of the embodiments, preferably, the control processfor the first mode is configured to control the power transmissioncircuit unit to, when the first charge rate is higher than thepredetermined threshold, if the required output is greater than the C-ththreshold, supply an amount of power supplied corresponding to adifference between the C-th threshold and the B-th threshold from thesecond energy storage device to the electrical load and supply from thefirst energy storage device to the electrical load an amount of powersupplied which is equal to a difference obtained by subtracting theamount of power supplied from the second energy storage device to theelectrical load from the amount of power supplied corresponding to therequired output (a ninth aspect of the embodiments).

According to this configuration, in the first mode, when the secondcharge rate is higher than the predetermined threshold, if the requiredoutput is greater than the C-th threshold, a large amount of power canbe supplied from both the first energy storage device and the secondenergy storage device to the electrical load so not to cause the load onthe first energy storage device and the second energy storage device tobecome excessive (and therefore to be able to minimize the progressionof deterioration of each energy storage device).

In the first to ninth aspects of the embodiments, preferably, thecontrol process for the first mode and the control process for thesecond mode include a process for controlling the power transmissioncircuit unit to, when a first charge rate that is a charge rate of thefirst energy storage device is in a predetermined range during aregenerative operation of the electrical load, use regenerative poweroutput from the electrical load to charge the first energy storagedevice more preferentially than the second energy storage device whilelimiting an amount of charging power of the first energy storage deviceto a value less than or equal to a predetermined value, and thepredetermined range of the first charge rate in the first mode isextended with respect to the predetermined range of the first chargerate in the second mode toward a side on which the first charge rateincreases (a tenth aspect of the embodiments).

According to this configuration, when power is supplied to theelectrical load, in the first mode, the first energy storage device ischargeable more preferentially than the second energy storage devicewithin a wider range of the first charge rate than that of the secondmode. This can minimize the reduction in the charge rate of the firstenergy storage device in the first mode. In this case, the amount ofregenerative power used to charge the first energy storage device islimited to a value less than or equal to a predetermined value. Thisenables the first energy storage device to be charged at a low rate andcan therefore suppress the progression of deterioration of the firstenergy storage device.

In the tenth aspect of the embodiments, when the first charge rate is inthe predetermined range, if the regenerative power exceeds thepredetermined value, the excess of the regenerative power can be used tocharge the second energy storage device. When the first charge rate isoutside the predetermined range, the regenerative power can be used topreferentially charge the second energy storage device.

In the first to tenth aspects of the embodiments, the power supplysystem may further include an electric generator capable of outputtinggenerated power by using motive power of an internal combustion engine,and the power transmission circuit unit may be configured to furtherhave a function of performing power transmission between the firstenergy storage device and the electric generator, between the secondenergy storage device and the electric generator, or between theelectrical load and the electric generator. In this case, preferably,the control device is configured to further have a function of executinga power generation control process in accordance with at least thesecond charge rate, the power generation control process being a processfor controlling the power transmission circuit unit to charge at leastthe second energy storage device, out of the first energy storage deviceand the second energy storage device, with the generated power of theelectric generator (an eleventh aspect of the embodiments).

This configuration allows the second energy storage device to be chargedwith the generated power of the electric generator at desired timing inaccordance with the charge rate of the second energy storage device.

In the eleventh aspect of the embodiments, preferably, the controldevice is configured to charge the second energy storage device with thegenerated power more preferentially than charging the first energystorage device with the generated power in the power generation controlprocess (a twelfth aspect of the embodiments).

Deterioration of the second energy storage device with relatively highpower density is less likely to progress even when the second energystorage device is charged at a comparatively higher rate (higher speed)than the first energy storage device. The twelfth aspect of theembodiments thus enables the second energy storage device to beefficiently charged with the generated power of the electric generator.That is, the charge rate of the second energy storage device can beefficiently restored. As a result, the period during which the electricgenerator performs a power generation operation by using the motivepower of the internal combustion engine can be minimized.

In particular, a combination of the twelfth aspect of the embodimentswith the fourth aspect of the embodiments allows the power generated bythe electric generator to be supplied via the second energy storagedevice to charge the first energy storage device. This enables the firstenergy storage device to be indirectly charged with the generated powerwhile suppressing the progression of deterioration of the first energystorage device.

The power supply system according to the first to twelfth aspects of theembodiments may further include an actuator that is the electrical load,an internal combustion engine, a driven load drivable by motive power ofat least one of the actuator and the internal combustion engine, and anelectric generator capable of outputting generated power by using motivepower of the internal combustion engine. In this case, preferably, thecontrol device is configured to further have a function of controllingthe power transmission circuit unit by using a charge-depleting (CD)mode and a charge-sustaining (CS) mode, the charge-depleting (CD) modebeing a mode in which only motive power of the actuator, out of theinternal combustion engine and the actuator, is usable as motive powerfor driving the driven load, the charge-sustaining (CS) mode being amode in which motive power of the internal combustion engine and motivepower of the actuator are usable as motive power for driving the drivenload, and to execute the control process for the first mode and thecontrol process for the second mode in the charge-sustaining (CS) mode(a thirteenth aspect of the embodiments).

When the thirteenth aspect of the embodiments is combined with the tenthor eleventh aspect of the embodiments, the internal combustion engineand the electric generator in the thirteenth aspect of the embodimentsare identical to the internal combustion engine and the electricgenerator in the eleventh aspect of the embodiments, respectively.

According to the thirteenth aspect of the embodiments, the respectivecontrol processes for the first mode and the second mode are executed ina charge-sustaining (CS) mode in which the motive power of the internalcombustion engine is usable as motive power for driving the driven load.This allows the respective control processes for the first mode and thesecond mode to be established by taking into account charging of thefirst energy storage device or the second energy storage device with thegenerated power. In addition, the load placed on an actuator serving asthe source of motive power for driving a driven load can be reduced.This can effectively prevent the power share to be supplied from thefirst energy storage device or the second energy storage device to theactuator from being excessive. As a result, the effect of suppressingthe progression of deterioration of the first energy storage device andthe second energy storage device can be enhanced.

In the first to thirteenth aspects of the embodiments described above,the electrical load or the actuator may be implemented as an electricmotor, for example. The power transmission circuit unit may have aconfiguration that includes, for example, a voltage converter thatconverts an output voltage of at least one of the first energy storagedevice and the second energy storage device and outputs the resultingvoltage, and an inverter that converts direct-current power input fromthe first energy storage device, the second energy storage device, orthe voltage converter into alternating-current power and supplies thealternating-current power to the electrical load or the actuator.

Further, a transportation apparatus according to an aspect of theembodiments disclosed herein includes the power supply system accordingto the first to thirteenth aspects of the embodiments (a fourteenthaspect of the embodiments). This transportation apparatus isimplementable as a transportation apparatus that achieves the advantagesdescribed above with reference to the first to thirteenth aspects of theembodiments.

Further, a method for controlling a power supply system according to anaspect of the embodiments disclosed herein is a method for controlling apower supply system, the power supply system including a first energystorage device, a second energy storage device having a higher powerdensity and a lower energy density than the first energy storage device,and a power transmission circuit unit having a function of performingpower transmission among an electrical load, the first energy storagedevice, and the second energy storage device, the electrical load beingoperated in response to power supplied from at least one of the firstenergy storage device and the second energy storage device. The methodincludes selecting a mode for controlling the power transmission circuitunit from a first mode and a second mode in accordance with a secondcharge rate that is a charge rate of the second energy storage device;and controlling the power transmission circuit unit to supply power fromat least one of the first energy storage device and the second energystorage device to the electrical load by performing a control processfor the selected mode, wherein the selecting is configured to select thesecond mode when the second charge rate decreases to a predeterminedfirst switching threshold while the first mode is selected, and toselect the first mode when the second charge rate increases to apredetermined second switching threshold higher than the first switchingthreshold while the second mode is selected, and a control process forthe second mode is configured to control the power transmission circuitunit in such a manner as to suppress discharge from the second energystorage device more than in a control process for the first mode (afifteenth aspect of the embodiments).

Thus, advantages similar to those of the first aspect of the embodimentsmay be achieved.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A power supply system comprising: a first energystorage having a first power density and a first energy density, a firstcharge rate indicating a charge rate of the first energy storage; asecond energy storage having a second power density higher than thefirst power density and a second energy density lower than the firstenergy density, a second charge rate indicating a charge rate of thesecond energy storage; a power transmission electric circuit via whichan electrical load is connected to the first energy storage and to thesecond energy storage; and circuitry configured to control the powertransmission electric circuit in a first mode when the second chargerate is higher than a second switching threshold while controlling thepower transmission electric circuit in a second mode, a ratio of a firstelectric power amount of an electric power to be supplied from the firstenergy storage to the electrical load and a second electric power amountof an electric power to be supplied from the second energy storage tothe electrical load being changed in accordance with the first chargerate at least in the first mode among the first mode and the secondmode, and control the power transmission electric circuit in the secondmode when the second charge rate is lower than a first switchingthreshold lower than the second switching threshold while controllingthe power transmission electric circuit in the first mode, the secondelectric power amount in the second mode being smaller than the secondelectric power amount in the first mode.
 2. The power supply systemaccording to claim 1, wherein the circuitry is configured to control thepower transmission electric circuit in the first mode and the secondmode to supply an electric power from at least one of the first energystorage and the second energy storage to the electrical load inaccordance with at least a required output of the electrical load, andwherein the circuitry is configured to control the power transmissionelectric circuit in the second unit so that a range of the requiredoutput within which the second energy storage is to supply an electricpower to the electrical load is smaller than a range of the requiredoutput within which the second energy storage is to supply an electricpower to the electrical load in the first mode.
 3. The power supplysystem according to claim 1, wherein the circuitry is configured tocontrol the power transmission electric circuit in the second mode todisable discharge from the second energy storage and to enable powersupply from the first energy storage to the electrical load.
 4. Thepower supply system according to claim 1, wherein the circuitry isconfigured to control the power transmission electric circuit when thefirst charge rate is lower than a first charge rate threshold in thefirst mode to output a base amount of an electric power from the secondenergy storage regardless of a required output of the electrical load tosupply an electrical load quota of the electric power out of the baseamount of the electric power to the electrical load in accordance withan required output of the electrical load, and charge the first energystorage with a charge quota of the electric power, the charge quotabeing obtained by subtracting the electrical load quota from the baseamount.
 5. The power supply system according to claim 4, wherein thecircuitry is configured to control the power transmission electriccircuit when the first charge rate is lower than the first charge ratethreshold in the first mode to supply an amount of the electric powercorresponding to the required output from only the second energy storageto the electrical load when the required output is greater than the baseamount and less than or equal to a first maximum supplying amount. 6.The power supply system according to claim 5, wherein the circuitry isconfigured to control the power transmission electric circuit when thefirst charge rate is lower than the first charge rate threshold and whenthe required output is greater than the first maximum supplying amountin the first mode to supply the first maximum supplying amount of theelectric power from the second energy storage to the electrical load,and supply a replenishment amount of an electric power from the firstenergy storage to the electrical load, the replenishment amountcorresponding to a difference between the required output and the firstmaximum supplying amount.
 7. The power supply system according to claim1, wherein the circuitry is configured to control the power transmissionelectric circuit when the first charge rate is higher than a firstcharge rate threshold in the first mode to supply an amount of theelectric power corresponding to the required output from only the firstenergy storage to the electrical load when a required output of theelectrical load is less than or equal to a second maximum supplyingamount.
 8. The power supply system according to claim 7, wherein thecircuitry is configured to control the power transmission electriccircuit when the first charge rate is higher than the first charge ratethreshold and when the required output is greater than the secondmaximum supplying amount and less than a sum of the second maximumsupplying amount and a third maximum supplying amount in the first modeto supply the second maximum supplying amount of the electric power fromthe first energy storage to the electrical load, and supply from thesecond energy storage to the electrical load, an amount of the electricpower corresponding to a difference between the required output and thesecond maximum supplying amount.
 9. The power supply system according toclaim 8, wherein the circuitry is configured to control the powertransmission electric circuit when the first charge rate is higher thanthe first change rate threshold and when the required output is greaterthan the sum of the second maximum supplying amount and the thirdmaximum supplying amount in the first mode to supply the third maximumsupplying amount of the electric power from the second energy storagedevice to the electrical load, and supply from the first energy storageto the electrical load, an amount of power supplied which is obtained bysubtracting the third maximum supplying amount from the required output.10. The power supply system according to claim 1, wherein the circuitryis configured to control the power transmission electric circuit whenthe first charge rate is in a charging priority range during aregenerative operation of the electrical load in the first mode and inthe second mode to use regenerative power output from the electricalload to charge the first energy storage more preferentially than thesecond energy storage while limiting an amount of charging power of thefirst energy storage to a value less than or equal to a charging powerthreshold, and wherein the charging priority range in the first mode isextended with respect to the charging priority range in the second modesuch that an upper limit of the charging priority range in the firstmode is larger than an upper limit of the charging priority range in thesecond mode.
 11. The power supply system according to claim 1, furthercomprising an electric generator to generate an electric power usingmotive power of an internal combustion engine, wherein the powertransmission electric circuit is configured to transmit the electricpower between the first energy storage and the electric generator,between the second energy storage and the electric generator, or betweenthe electrical load and the electric generator, and wherein thecircuitry is configured to control the power transmission electriccircuit to charge at least the second energy storage among the firstenergy storage and the second energy storage with the electric powergenerated in the electric generator in accordance with at least thesecond charge rate.
 12. The power supply system according to claim 11,wherein the circuitry is configured to charge the second energy storagewith the electric power generated in the electric generator morepreferentially than to charge the first energy storage with the electricpower generated in the electric generator.
 13. The power supply systemaccording to claim 1, further comprising: an actuator to work as theelectrical load; an internal combustion engine; and a driven load to bedriven by at least one of the actuator and the internal combustionengine, wherein the circuitry is configured to control the powertransmission electric circuit to use only motive power of the actuatorto drive the driven load in a charge-depleting mode and to use motivepower of both the internal combustion engine and the actuator to drivethe driven load in a charge-sustaining mode, and wherein thecharge-sustaining mode includes the first mode and the second mode. 14.A transportation apparatus comprising the power supply system accordingto claim
 1. 15. A method for controlling a power supply system,comprising: detecting a first charge rate of a first energy storagehaving a first power density and a first energy density; detecting asecond charge rate of a second energy storage having a second powerdensity higher than the first power density and a second energy densitylower than the first energy density; controlling an power transmissionelectric circuit in a first mode when the second charge rate is higherthan a second switching threshold while the power transmission electriccircuit is controlled in a second mode, a ratio of a first electricpower amount of an electric power to be supplied from the first energystorage to an electrical load and a second electric power amount of anelectric power to be supplied from the second energy storage to theelectrical load being changed in accordance with the first charge rateat least in the first mode among the first mode and the second mode, theelectrical load being connected to the first energy storage and thesecond energy storage via the power transmission electric circuit; andcontrolling the power transmission electric circuit in the second modewhen the second charge rate is lower than a first switching thresholdlower than the second switching threshold while the power transmissionelectric circuit is controlled in the first mode, the second electricpower amount in the second mode being smaller than the second electricpower amount in the first mode.